diff --git a/Gemfile b/Gemfile
index eb55e3a..a42fad6 100644
--- a/Gemfile
+++ b/Gemfile
@@ -8,6 +8,7 @@ ruby "2.7.4"
 gem "pg", "~> 1.1"
 gem "puma", "~> 5.0"
 gem "rails", "~> 6.1.4"
+gem "rails-i18n", "~> 6.0"
 gem "sass-rails", ">= 6"
 gem "turbolinks", "~> 5"
 gem "webpacker", "~> 5.0"
diff --git a/Gemfile.lock b/Gemfile.lock
index 0f7b1f1..e0b38e7 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -216,6 +216,9 @@ GEM
       ruby-graphviz (~> 1.2)
     rails-html-sanitizer (1.3.0)
       loofah (~> 2.3)
+    rails-i18n (6.0.0)
+      i18n (>= 0.7, < 2)
+      railties (>= 6.0.0, < 7)
     railties (6.1.4)
       actionpack (= 6.1.4)
       activesupport (= 6.1.4)
@@ -351,6 +354,7 @@ DEPENDENCIES
   pundit
   rails (~> 6.1.4)
   rails-erd
+  rails-i18n (~> 6.0)
   rspec-graphql_matchers (~> 1.3)
   rspec-rails
   rubocop-rails
diff --git a/app/graphql/inputs/create_buy_crypto_order_attributes_input.rb b/app/graphql/inputs/create_buy_crypto_order_attributes_input.rb
new file mode 100644
index 0000000..3b3f37e
--- /dev/null
+++ b/app/graphql/inputs/create_buy_crypto_order_attributes_input.rb
@@ -0,0 +1,7 @@
+# frozen_string_literal: true
+module Inputs
+  class CreateBuyCryptoOrderAttributesInput < Types::BaseInputObject
+    argument :currency_id, ID, required: true
+    argument :amount_cents, Integer, "Amount to be paid", required: true
+  end
+end
diff --git a/app/graphql/inputs/create_sell_crypto_order_attributes_input.rb b/app/graphql/inputs/create_sell_crypto_order_attributes_input.rb
new file mode 100644
index 0000000..e6da70f
--- /dev/null
+++ b/app/graphql/inputs/create_sell_crypto_order_attributes_input.rb
@@ -0,0 +1,7 @@
+# frozen_string_literal: true
+module Inputs
+  class CreateSellCryptoOrderAttributesInput < Types::BaseInputObject
+    argument :currency_id, ID, required: true
+    argument :amount, String, "Amount to be paid", required: true
+  end
+end
diff --git a/app/graphql/mutations/base_mutation.rb b/app/graphql/mutations/base_mutation.rb
index e589946..207afde 100644
--- a/app/graphql/mutations/base_mutation.rb
+++ b/app/graphql/mutations/base_mutation.rb
@@ -6,8 +6,16 @@ module Mutations
     input_object_class Types::BaseInputObject
     object_class Types::BaseObject
 
-    field :errors, [String],
+    field :errors, [Types::RecordInvalidType],
       null: true,
       description: "Errors encountered during execution of the mutation."
+
+    def current_user
+      context[:current_user]
+    end
+
+    def decode_id(encoded_id)
+      GraphQL::Schema::UniqueWithinType.decode(encoded_id).last
+    end
   end
 end
diff --git a/app/graphql/mutations/create_buy_crypto_order.rb b/app/graphql/mutations/create_buy_crypto_order.rb
new file mode 100644
index 0000000..9efb152
--- /dev/null
+++ b/app/graphql/mutations/create_buy_crypto_order.rb
@@ -0,0 +1,26 @@
+# frozen_string_literal: true
+module Mutations
+  class CreateBuyCryptoOrder < BaseMutation
+    field :order, Types::BuyCryptoOrderType, null: true
+
+    argument :order, Inputs::CreateBuyCryptoOrderAttributesInput, required: true
+
+    def resolve(order:)
+      currency_id = decode_id(order[:currency_id])
+
+      ActiveRecord::Base.transaction do
+        current_user.fiat_balance.withdrawal!(order[:amount_cents])
+
+        record = BuyCryptoOrder.create!(
+          paid_amount_cents: order[:amount_cents],
+          currency_id: currency_id,
+          user_id: current_user.id,
+        )
+
+        { order: record }
+      rescue ActiveRecord::RecordInvalid => e
+        { errors: Resolvers::ModelErrors.from_active_record_model(e.record) }
+      end
+    end
+  end
+end
diff --git a/app/graphql/mutations/create_sell_crypto_order.rb b/app/graphql/mutations/create_sell_crypto_order.rb
new file mode 100644
index 0000000..9b70114
--- /dev/null
+++ b/app/graphql/mutations/create_sell_crypto_order.rb
@@ -0,0 +1,28 @@
+# frozen_string_literal: true
+module Mutations
+  class CreateSellCryptoOrder < BaseMutation
+    field :order, Types::SellCryptoOrderType, null: true
+
+    argument :order, Inputs::CreateSellCryptoOrderAttributesInput, required: true
+
+    def resolve(order:)
+      currency_id = decode_id(order[:currency_id])
+      amount = BigDecimal(order[:amount])
+
+      ActiveRecord::Base.transaction do
+        current_user.balances.find_by!(currency_id: currency_id)
+          .withdrawal!(amount)
+
+        record = SellCryptoOrder.create(
+          paid_amount: amount,
+          currency_id: currency_id,
+          user_id: current_user.id,
+        )
+
+        { order: record }
+      rescue ActiveRecord::RecordInvalid => e
+        { errors: Resolvers::ModelErrors.from_active_record_model(e.record) }
+      end
+    end
+  end
+end
diff --git a/app/graphql/resolvers/model_errors.rb b/app/graphql/resolvers/model_errors.rb
new file mode 100644
index 0000000..8156a01
--- /dev/null
+++ b/app/graphql/resolvers/model_errors.rb
@@ -0,0 +1,39 @@
+# frozen_string_literal: true
+module Resolvers
+  class ModelErrors
+    attr_reader :full_messages, :field_name, :messages, :path
+
+    def initialize(args)
+      @full_messages = args[:full_messages]
+      @field_name = args[:field_name]
+      @messages = args[:messages]
+      @path = args[:path]
+    end
+
+    def self.from_active_record_model(model)
+      return if model&.errors.blank?
+
+      model.errors.messages.map do |field, messages|
+        new(
+          full_messages: model.errors.full_messages_for(field),
+          field_name: field,
+          messages: messages,
+          path: ["attributes", field]
+        )
+      end
+    end
+
+    def self.from_active_record_model_errors(errors)
+      return if errors.blank?
+
+      errors.messages.map do |field, messages|
+        new(
+          full_messages: errors.full_messages_for(field),
+          field_name: field,
+          messages: messages,
+          path: ["attributes", field]
+        )
+      end
+    end
+  end
+end
diff --git a/app/graphql/types/buy_crypto_order_type.rb b/app/graphql/types/buy_crypto_order_type.rb
new file mode 100644
index 0000000..1c28420
--- /dev/null
+++ b/app/graphql/types/buy_crypto_order_type.rb
@@ -0,0 +1,22 @@
+# frozen_string_literal: true
+module Types
+  class BuyCryptoOrderType < Types::BaseObject
+    implements GraphQL::Types::Relay::Node
+    global_id_field :id
+
+    graphql_name "BuyCryptoOrder"
+
+    field :id, ID, null: false
+
+    field :currency, CurrencyType, null: false
+    def currency
+      dataloader.with(Dataloader::Source, Currency).load(object.currency_id)
+    end
+
+    field :status, ProcessStatusEnum, null: false
+    field :paid_amount_cents, Integer, null: false
+    field :received_amount, String, null: true
+    field :created_at, GraphQL::Types::ISO8601DateTime, null: false
+    field :updated_at, GraphQL::Types::ISO8601DateTime, null: false
+  end
+end
diff --git a/app/graphql/types/fiat_balance_type.rb b/app/graphql/types/fiat_balance_type.rb
index 65eaa24..be79b3e 100644
--- a/app/graphql/types/fiat_balance_type.rb
+++ b/app/graphql/types/fiat_balance_type.rb
@@ -9,7 +9,5 @@ module Types
     field :id, ID, null: false
     field :amount_cents, Integer, null: false
     field :amount_currency, String, null: false
-    field :created_at, GraphQL::Types::ISO8601DateTime, null: false
-    field :updated_at, GraphQL::Types::ISO8601DateTime, null: false
   end
 end
diff --git a/app/graphql/types/mutation_type.rb b/app/graphql/types/mutation_type.rb
index c928833..a1405bb 100644
--- a/app/graphql/types/mutation_type.rb
+++ b/app/graphql/types/mutation_type.rb
@@ -1,5 +1,7 @@
 # frozen_string_literal: true
 module Types
   class MutationType < Types::BaseObject
+    field :create_sell_crypto_order, mutation: Mutations::CreateSellCryptoOrder
+    field :create_buy_crypto_order, mutation: Mutations::CreateBuyCryptoOrder
   end
 end
diff --git a/app/graphql/types/process_status_enum.rb b/app/graphql/types/process_status_enum.rb
new file mode 100644
index 0000000..9d5704c
--- /dev/null
+++ b/app/graphql/types/process_status_enum.rb
@@ -0,0 +1,10 @@
+# frozen_string_literal: true
+module Types
+  class ProcessStatusEnum < Types::BaseEnum
+    graphql_name "ProcessStatus"
+
+    value "PROCESSING", value: "processing"
+    value "COMPLETED", value: "completed"
+    value "CANCELED", value: "canceled"
+  end
+end
diff --git a/app/graphql/types/query_type.rb b/app/graphql/types/query_type.rb
index a87b9e2..480509a 100644
--- a/app/graphql/types/query_type.rb
+++ b/app/graphql/types/query_type.rb
@@ -18,5 +18,15 @@ module Types
     def fiat_balances
       Pundit.policy_scope(current_user, FiatBalance)
     end
+
+    field :sell_crypto_orders, SellCryptoOrderType.connection_type, null: false
+    def sell_crypto_orders
+      []
+    end
+
+    field :buy_crypto_orders, BuyCryptoOrderType.connection_type, null: false
+    def buy_crypto_orders
+      []
+    end
   end
 end
diff --git a/app/graphql/types/record_invalid_type.rb b/app/graphql/types/record_invalid_type.rb
new file mode 100644
index 0000000..42ea150
--- /dev/null
+++ b/app/graphql/types/record_invalid_type.rb
@@ -0,0 +1,11 @@
+# frozen_string_literal: true
+
+module Types
+  class RecordInvalidType < Types::BaseObject
+    graphql_name "RecordInvalid"
+    field :full_messages, [String], null: false
+    field :field_name, String, null: true
+    field :messages, [String], null: true
+    field :path, [String], null: true
+  end
+end
diff --git a/app/graphql/types/sell_crypto_order_type.rb b/app/graphql/types/sell_crypto_order_type.rb
new file mode 100644
index 0000000..c70bcde
--- /dev/null
+++ b/app/graphql/types/sell_crypto_order_type.rb
@@ -0,0 +1,22 @@
+# frozen_string_literal: true
+module Types
+  class SellCryptoOrderType < Types::BaseObject
+    implements GraphQL::Types::Relay::Node
+    global_id_field :id
+
+    graphql_name "SellCryptoOrder"
+
+    field :id, ID, null: false
+
+    field :currency, CurrencyType, null: false
+    def currency
+      dataloader.with(Dataloader::Source, Currency).load(object.currency_id)
+    end
+
+    field :status, ProcessStatusEnum, null: false
+    field :paid_amount, String, null: false
+    field :received_amount_cents, Integer, null: true
+    field :created_at, GraphQL::Types::ISO8601DateTime, null: false
+    field :updated_at, GraphQL::Types::ISO8601DateTime, null: false
+  end
+end
diff --git a/app/graphql/x_stake_schema.rb b/app/graphql/x_stake_schema.rb
index e95c99a..e7c28a0 100644
--- a/app/graphql/x_stake_schema.rb
+++ b/app/graphql/x_stake_schema.rb
@@ -1,6 +1,6 @@
 # frozen_string_literal: true
 class XStakeSchema < GraphQL::Schema
-  # mutation(Types::MutationType)
+  mutation(Types::MutationType)
   query(Types::QueryType)
   use GraphQL::Dataloader
 
diff --git a/app/javascript/__generated__/schema.graphql b/app/javascript/__generated__/schema.graphql
index c945e2f..16763b3 100644
--- a/app/javascript/__generated__/schema.graphql
+++ b/app/javascript/__generated__/schema.graphql
@@ -34,19 +34,24 @@ type BalanceEdge {
   node: Balance!
 }
 
-type Currency implements Node {
+type BuyCryptoOrder implements Node {
+  createdAt: ISO8601DateTime!
+  currency: Currency!
   id: ID!
-  name: String!
+  paidAmountCents: Int!
+  receivedAmount: Float
+  status: ProcessStatus!
+  updatedAt: ISO8601DateTime!
 }
 
 """
-The connection type for Currency.
+The connection type for BuyCryptoOrder.
 """
-type CurrencyConnection {
+type BuyCryptoOrderConnection {
   """
   A list of edges.
   """
-  edges: [CurrencyEdge!]!
+  edges: [BuyCryptoOrderEdge!]!
 
   """
   Information to aid in pagination.
@@ -57,7 +62,7 @@ type CurrencyConnection {
 """
 An edge in a connection.
 """
-type CurrencyEdge {
+type BuyCryptoOrderEdge {
   """
   A cursor for use in pagination.
   """
@@ -66,7 +71,82 @@ type CurrencyEdge {
   """
   The item at the end of the edge.
   """
-  node: Currency!
+  node: BuyCryptoOrder!
+}
+
+input CreateBuyCryptoOrderAttributesInput {
+  """
+  Amount to be paid
+  """
+  amount: Float!
+  currencyId: ID!
+}
+
+"""
+Autogenerated input type of CreateBuyCryptoOrder
+"""
+input CreateBuyCryptoOrderInput {
+  """
+  A unique identifier for the client performing the mutation.
+  """
+  clientMutationId: String
+  order: CreateBuyCryptoOrderAttributesInput!
+}
+
+"""
+Autogenerated return type of CreateBuyCryptoOrder
+"""
+type CreateBuyCryptoOrderPayload {
+  """
+  A unique identifier for the client performing the mutation.
+  """
+  clientMutationId: String
+
+  """
+  Errors encountered during execution of the mutation.
+  """
+  errors: [String!]
+  order: BuyCryptoOrder!
+}
+
+input CreateSellCryptoOrderAttributesInput {
+  """
+  Amount to be paid
+  """
+  amount: Float!
+  currencyId: ID!
+}
+
+"""
+Autogenerated input type of CreateSellCryptoOrder
+"""
+input CreateSellCryptoOrderInput {
+  """
+  A unique identifier for the client performing the mutation.
+  """
+  clientMutationId: String
+  order: CreateSellCryptoOrderAttributesInput!
+}
+
+"""
+Autogenerated return type of CreateSellCryptoOrder
+"""
+type CreateSellCryptoOrderPayload {
+  """
+  A unique identifier for the client performing the mutation.
+  """
+  clientMutationId: String
+
+  """
+  Errors encountered during execution of the mutation.
+  """
+  errors: [String!]
+  order: SellCryptoOrder!
+}
+
+type Currency implements Node {
+  id: ID!
+  name: String!
 }
 
 type FiatBalance implements Node {
@@ -112,6 +192,21 @@ An ISO 8601-encoded datetime
 """
 scalar ISO8601DateTime
 
+type Mutation {
+  createBuyCryptoOrder(
+    """
+    Parameters for CreateBuyCryptoOrder
+    """
+    input: CreateBuyCryptoOrderInput!
+  ): CreateBuyCryptoOrderPayload
+  createSellCryptoOrder(
+    """
+    Parameters for CreateSellCryptoOrder
+    """
+    input: CreateSellCryptoOrderInput!
+  ): CreateSellCryptoOrderPayload
+}
+
 """
 An object with an ID.
 """
@@ -147,6 +242,12 @@ type PageInfo {
   startCursor: String
 }
 
+enum ProcessStatus {
+  CANCELED
+  COMPLETED
+  PROCESSING
+}
+
 type Query {
   balances(
     """
@@ -169,7 +270,7 @@ type Query {
     """
     last: Int
   ): BalanceConnection!
-  currencies(
+  buyCryptoOrders(
     """
     Returns the elements in the list that come after the specified cursor.
     """
@@ -189,7 +290,7 @@ type Query {
     Returns the last _n_ elements from the list.
     """
     last: Int
-  ): CurrencyConnection!
+  ): BuyCryptoOrderConnection!
   currentUser: User
   fiatBalances(
     """
@@ -232,6 +333,67 @@ type Query {
     """
     ids: [ID!]!
   ): [Node]!
+  sellCryptoOrders(
+    """
+    Returns the elements in the list that come after the specified cursor.
+    """
+    after: String
+
+    """
+    Returns the elements in the list that come before the specified cursor.
+    """
+    before: String
+
+    """
+    Returns the first _n_ elements from the list.
+    """
+    first: Int
+
+    """
+    Returns the last _n_ elements from the list.
+    """
+    last: Int
+  ): SellCryptoOrderConnection!
+}
+
+type SellCryptoOrder implements Node {
+  createdAt: ISO8601DateTime!
+  currency: Currency!
+  id: ID!
+  paidAmount: Float!
+  receivedAmountCents: Int
+  status: ProcessStatus!
+  updatedAt: ISO8601DateTime!
+}
+
+"""
+The connection type for SellCryptoOrder.
+"""
+type SellCryptoOrderConnection {
+  """
+  A list of edges.
+  """
+  edges: [SellCryptoOrderEdge!]!
+
+  """
+  Information to aid in pagination.
+  """
+  pageInfo: PageInfo!
+}
+
+"""
+An edge in a connection.
+"""
+type SellCryptoOrderEdge {
+  """
+  A cursor for use in pagination.
+  """
+  cursor: String!
+
+  """
+  The item at the end of the edge.
+  """
+  node: SellCryptoOrder!
 }
 
 type User {
diff --git a/app/models/balance.rb b/app/models/balance.rb
index 8dfc70b..7f98371 100644
--- a/app/models/balance.rb
+++ b/app/models/balance.rb
@@ -25,5 +25,13 @@ class Balance < ApplicationRecord
   belongs_to :user
   belongs_to :currency
 
-  validates :amount, presence: true
+  validates :amount, presence: true, numericality: { greater_than_or_equal_to: 0 }
+
+  def withdrawal!(value)
+    update!(amount: amount - value)
+  end
+
+  def deposit!(value)
+    update!(amount: amount + value)
+  end
 end
diff --git a/app/models/fiat_balance.rb b/app/models/fiat_balance.rb
index 8722278..b64c62a 100644
--- a/app/models/fiat_balance.rb
+++ b/app/models/fiat_balance.rb
@@ -24,7 +24,17 @@ class FiatBalance < ApplicationRecord
 
   monetize :amount_cents
 
+  validates :amount_cents, numericality: { greater_than_or_equal_to: 0 }
+
   def amount_formatted
     amount.format
   end
+
+  def withdrawal!(value)
+    update!(amount_cents: amount_cents - value)
+  end
+
+  def deposit!(value)
+    update!(amount_cents: amount_cents + value)
+  end
 end
diff --git a/app/models/user.rb b/app/models/user.rb
index cbc1d8d..26d827a 100644
--- a/app/models/user.rb
+++ b/app/models/user.rb
@@ -25,7 +25,7 @@ class User < ApplicationRecord
     :recoverable, :rememberable, :validatable
 
   has_many :documents, class_name: "UserDocument", dependent: :destroy
-  has_one :balance, dependent: :restrict_with_error
+  has_many :balances, dependent: :restrict_with_error
   has_one :fiat_balance, dependent: :restrict_with_error
 
   validates :first_name, :last_name, :email, presence: true
diff --git a/config/locales/activerecord.yml b/config/locales/pt-BR.yml
similarity index 66%
rename from config/locales/activerecord.yml
rename to config/locales/pt-BR.yml
index 03538e7..ee233df 100644
--- a/config/locales/activerecord.yml
+++ b/config/locales/pt-BR.yml
@@ -32,6 +32,18 @@ pt-BR:
 
       fiat_balance:
         amount_formatted: Quantia
+        amount_cents: Quantia
 
       currency:
-        name: Nome
\ No newline at end of file
+        name: Nome
+
+    errors:
+      models:
+        balance:
+          attributes:
+            amount:
+              greater_than_or_equal_to: "saldo insuficiente"
+        fiat_balance:
+          attributes:
+            amount_cents:
+              greater_than_or_equal_to: "saldo insuficiente"
\ No newline at end of file
diff --git a/spec/factories/fiat_balances.rb b/spec/factories/fiat_balances.rb
index 37ac2a4..307c2bb 100644
--- a/spec/factories/fiat_balances.rb
+++ b/spec/factories/fiat_balances.rb
@@ -23,6 +23,6 @@ FactoryBot.define do
   factory :fiat_balance do
     association :user
     amount_currency { "BRL" }
-    amount_cents { Faker::Number.number(digits: 10) }
+    amount_cents { Faker::Number.number(digits: 4) }
   end
 end
diff --git a/spec/graphql/inputs/create_buy_crypto_order_attributes_input_spec.rb b/spec/graphql/inputs/create_buy_crypto_order_attributes_input_spec.rb
new file mode 100644
index 0000000..84a1cbc
--- /dev/null
+++ b/spec/graphql/inputs/create_buy_crypto_order_attributes_input_spec.rb
@@ -0,0 +1,12 @@
+# frozen_string_literal: true
+
+require "rails_helper"
+
+describe Inputs::CreateBuyCryptoOrderAttributesInput do
+  subject { described_class }
+
+  describe "fields" do
+    it { is_expected.to(accept_argument("currency_id").of_type("ID!")) }
+    it { is_expected.to(accept_argument("amount_cents").of_type("Int!")) }
+  end
+end
diff --git a/spec/graphql/inputs/create_sell_crypto_order_attributes_input_spec.rb b/spec/graphql/inputs/create_sell_crypto_order_attributes_input_spec.rb
new file mode 100644
index 0000000..84607d7
--- /dev/null
+++ b/spec/graphql/inputs/create_sell_crypto_order_attributes_input_spec.rb
@@ -0,0 +1,12 @@
+# frozen_string_literal: true
+
+require "rails_helper"
+
+describe Inputs::CreateSellCryptoOrderAttributesInput do
+  subject { described_class }
+
+  describe "fields" do
+    it { is_expected.to(accept_argument("currency_id").of_type("ID!")) }
+    it { is_expected.to(accept_argument("amount").of_type("String!")) }
+  end
+end
diff --git a/spec/graphql/mutations/create_buy_crypto_order_spec.rb b/spec/graphql/mutations/create_buy_crypto_order_spec.rb
new file mode 100644
index 0000000..86ebbb5
--- /dev/null
+++ b/spec/graphql/mutations/create_buy_crypto_order_spec.rb
@@ -0,0 +1,121 @@
+# frozen_string_literal: true
+
+require "rails_helper"
+
+RSpec.describe(Mutations::CreateBuyCryptoOrder, type: :mutation) do
+  let(:query_string) do
+    <<~GQL
+      mutation($currencyId: ID!, $amountCents: Int!) {
+        createBuyCryptoOrder(input: {
+          order: {
+            currencyId: $currencyId,
+            amountCents: $amountCents,
+          }
+        }) {
+          errors {
+            fullMessages
+            fieldName
+            messages
+            path
+          }
+          order {
+            status
+            paidAmountCents
+            receivedAmount
+            currency {
+              name
+            }
+          }
+        }
+      }
+    GQL
+  end
+
+  context "when the user has enough balance" do
+    it "withdraws from his account and creates a buy order" do
+      currency = create(:currency)
+      user = create(
+        :user,
+        fiat_balance: build(
+          :fiat_balance,
+          amount_cents: 100_00
+        ),
+      )
+
+      currency_global_id = GraphQL::Schema::UniqueWithinType.encode("Currency", currency.id)
+
+      variables = {
+        "currencyId": currency_global_id,
+        "amountCents": 90_00,
+      }
+
+      context = { current_user: user }
+
+      result = XStakeSchema.execute(
+        query_string,
+        variables: variables,
+        context: context
+      ).to_h.with_indifferent_access
+
+      expect(result).to(eq({
+        "data" => {
+          "createBuyCryptoOrder" => {
+            "errors" => nil,
+            "order" => {
+              "status" => "PROCESSING",
+              "paidAmountCents" => 90_00,
+              "receivedAmount" => nil,
+              "currency" => {
+                "name" => "CAKE",
+              },
+            },
+          },
+        },
+      }))
+
+      expect(user.fiat_balance.reload.amount_cents).to(eq(10_00))
+    end
+  end
+
+  context "when the user does not have enough balance" do
+    it "returns withdrawl error" do
+      currency = create(:currency)
+      user = create(
+        :user,
+        fiat_balance: build(
+          :fiat_balance,
+          amount_cents: 80_00
+        ),
+      )
+
+      currency_global_id = GraphQL::Schema::UniqueWithinType.encode("Currency", currency.id)
+
+      variables = {
+        "currencyId": currency_global_id,
+        "amountCents": 90_00,
+      }
+
+      context = { current_user: user }
+
+      result = XStakeSchema.execute(
+        query_string,
+        variables: variables,
+        context: context
+      ).to_h.with_indifferent_access
+
+      expect(result).to(eq({
+        "data" => {
+          "createBuyCryptoOrder" => {
+            "errors" => [{
+              "fullMessages" => ["Quantia saldo insuficiente"],
+              "fieldName" => "amount_cents",
+              "messages" => ["saldo insuficiente"],
+              "path" => ["attributes", "amount_cents"],
+            }],
+            "order" => nil,
+          },
+        },
+      }))
+    end
+  end
+end
diff --git a/spec/graphql/mutations/create_sell_crypto_order_spec.rb b/spec/graphql/mutations/create_sell_crypto_order_spec.rb
new file mode 100644
index 0000000..b817e14
--- /dev/null
+++ b/spec/graphql/mutations/create_sell_crypto_order_spec.rb
@@ -0,0 +1,121 @@
+# frozen_string_literal: true
+
+require "rails_helper"
+
+RSpec.describe(Mutations::CreateSellCryptoOrder, type: :mutation) do
+  let(:query_string) do
+    <<~GQL
+      mutation($currencyId: ID!, $amount: String!) {
+        createSellCryptoOrder(input: {
+          order: {
+            currencyId: $currencyId,
+            amount: $amount,
+          }
+        }) {
+          errors {
+            fullMessages
+            fieldName
+            messages
+            path
+          }
+          order {
+            status
+            paidAmount
+            receivedAmountCents
+            currency {
+              name
+            }
+          }
+        }
+      }
+    GQL
+  end
+
+  context "when the user has enough balance" do
+    it "withdraws from his account and creates a buy order" do
+      currency = create(:currency)
+      user = create(
+        :user,
+        balances: [
+          build(:balance, currency: currency, amount: 1.0034),
+        ]
+      )
+
+      currency_global_id = GraphQL::Schema::UniqueWithinType.encode("Currency", currency.id)
+
+      variables = {
+        "currencyId": currency_global_id,
+        "amount": "0.80",
+      }
+
+      context = { current_user: user }
+
+      result = XStakeSchema.execute(
+        query_string,
+        variables: variables,
+        context: context
+      ).to_h.with_indifferent_access
+
+      expect(result).to(eq({
+        "data" => {
+          "createSellCryptoOrder" => {
+            "errors" => nil,
+            "order" => {
+              "status" => "PROCESSING",
+              "paidAmount" => "0.8",
+              "receivedAmountCents" => nil,
+              "currency" => {
+                "name" => "CAKE",
+              },
+            },
+          },
+        },
+      }))
+
+      expect(user.balances.first.reload.amount.to_s).to(eq("0.2034"))
+    end
+  end
+
+  context "when the user does not have enough balance" do
+    it "returns withdrawl error" do
+      currency = create(:currency)
+      user = create(
+        :user,
+        balances: [
+          build(:balance, currency: currency, amount: 0.0034),
+        ]
+      )
+
+      currency_global_id = GraphQL::Schema::UniqueWithinType.encode("Currency", currency.id)
+
+      variables = {
+        "currencyId": currency_global_id,
+        "amount": "0.80",
+      }
+
+      context = { current_user: user }
+
+      result = XStakeSchema.execute(
+        query_string,
+        variables: variables,
+        context: context
+      ).to_h.with_indifferent_access
+
+      expect(result).to(eq({
+        "data" => {
+          "createSellCryptoOrder" => {
+            "errors" => [{
+              "fullMessages" => ["Quantia saldo insuficiente"],
+              "fieldName" => "amount",
+              "messages" => ["saldo insuficiente"],
+              "path" => ["attributes", "amount"],
+            }],
+            "order" => nil,
+          },
+        },
+      }))
+
+      expect(user.balances.first.reload.amount.to_s).to(eq("0.0034"))
+    end
+  end
+end
diff --git a/spec/graphql/types/buy_crypto_order_type_spec.rb b/spec/graphql/types/buy_crypto_order_type_spec.rb
new file mode 100644
index 0000000..27ed225
--- /dev/null
+++ b/spec/graphql/types/buy_crypto_order_type_spec.rb
@@ -0,0 +1,16 @@
+# frozen_string_literal: true
+require "rails_helper"
+
+RSpec.describe(Types::BuyCryptoOrderType) do
+  subject { described_class }
+
+  describe "arguments" do
+    it { is_expected.to(have_a_field(:id).of_type("ID!")) }
+    it { is_expected.to(have_a_field(:currency).of_type("Currency!")) }
+    it { is_expected.to(have_a_field(:paid_amount_cents).of_type("Int!")) }
+    it { is_expected.to(have_a_field(:received_amount).of_type("String")) }
+    it { is_expected.to(have_a_field(:status).of_type("ProcessStatus!")) }
+    it { is_expected.to(have_a_field(:created_at).of_type("ISO8601DateTime!")) }
+    it { is_expected.to(have_a_field(:updated_at).of_type("ISO8601DateTime!")) }
+  end
+end
diff --git a/spec/graphql/types/process_status_enum_spec.rb b/spec/graphql/types/process_status_enum_spec.rb
new file mode 100644
index 0000000..8bcb0c5
--- /dev/null
+++ b/spec/graphql/types/process_status_enum_spec.rb
@@ -0,0 +1,9 @@
+# frozen_string_literal: true
+
+require "rails_helper"
+
+describe Types::ProcessStatusEnum do
+  describe "values" do
+    it { expect(described_class.values.keys).to(match(["PROCESSING", "COMPLETED", "CANCELED"])) }
+  end
+end
diff --git a/spec/graphql/types/record_invalid_type_spec.rb b/spec/graphql/types/record_invalid_type_spec.rb
new file mode 100644
index 0000000..98416ce
--- /dev/null
+++ b/spec/graphql/types/record_invalid_type_spec.rb
@@ -0,0 +1,14 @@
+# frozen_string_literal: true
+
+require "rails_helper"
+
+describe Types::RecordInvalidType do
+  subject { described_class }
+
+  describe "fields" do
+    it { is_expected.to(have_field(:full_messages).of_type("[String!]!")) }
+    it { is_expected.to(have_field(:field_name).of_type("String")) }
+    it { is_expected.to(have_field(:messages).of_type("[String!]")) }
+    it { is_expected.to(have_field(:path).of_type("[String!]")) }
+  end
+end
diff --git a/spec/graphql/types/sell_crypto_order_type_spec.rb b/spec/graphql/types/sell_crypto_order_type_spec.rb
new file mode 100644
index 0000000..65b2e67
--- /dev/null
+++ b/spec/graphql/types/sell_crypto_order_type_spec.rb
@@ -0,0 +1,16 @@
+# frozen_string_literal: true
+require "rails_helper"
+
+RSpec.describe(Types::SellCryptoOrderType) do
+  subject { described_class }
+
+  describe "arguments" do
+    it { is_expected.to(have_a_field(:id).of_type("ID!")) }
+    it { is_expected.to(have_a_field(:currency).of_type("Currency!")) }
+    it { is_expected.to(have_a_field(:paid_amount).of_type("String!")) }
+    it { is_expected.to(have_a_field(:received_amount_cents).of_type("Int")) }
+    it { is_expected.to(have_a_field(:status).of_type("ProcessStatus!")) }
+    it { is_expected.to(have_a_field(:created_at).of_type("ISO8601DateTime!")) }
+    it { is_expected.to(have_a_field(:updated_at).of_type("ISO8601DateTime!")) }
+  end
+end
diff --git a/spec/models/admin_user_spec.rb b/spec/models/admin_user_spec.rb
deleted file mode 100644
index a6218ff..0000000
--- a/spec/models/admin_user_spec.rb
+++ /dev/null
@@ -1,25 +0,0 @@
-# frozen_string_literal: true
-
-# == Schema Information
-#
-# Table name: admin_users
-#
-#  id                     :bigint           not null, primary key
-#  email                  :string           default(""), not null
-#  encrypted_password     :string           default(""), not null
-#  remember_created_at    :datetime
-#  reset_password_sent_at :datetime
-#  reset_password_token   :string
-#  created_at             :datetime         not null
-#  updated_at             :datetime         not null
-#
-# Indexes
-#
-#  index_admin_users_on_email                 (email) UNIQUE
-#  index_admin_users_on_reset_password_token  (reset_password_token) UNIQUE
-#
-require "rails_helper"
-
-RSpec.describe(AdminUser, type: :model) do
-  pending "add some examples to (or delete) #{__FILE__}"
-end
diff --git a/spec/models/balance_spec.rb b/spec/models/balance_spec.rb
index 67694fc..0a3c3cf 100644
--- a/spec/models/balance_spec.rb
+++ b/spec/models/balance_spec.rb
@@ -32,4 +32,32 @@ RSpec.describe(Balance, type: :model) do
     it { is_expected.to(belong_to(:user)) }
     it { is_expected.to(belong_to(:currency)) }
   end
+
+  describe ".withdrwal!" do
+    context "when value is greater than the balance" do
+      it "raise ActiveRecord::RecordInvalid" do
+        balance = build(:balance, amount: 70.342)
+
+        expect { balance.withdrawal!(80) }.to(
+          raise_error(ActiveRecord::RecordInvalid, "A validação falhou: Quantia saldo insuficiente")
+        )
+      end
+    end
+
+    context "when value is equals to the balance" do
+      it "returns true" do
+        balance = build(:balance, amount: 70.342)
+
+        expect(balance.withdrawal!(70.342)).to(eq(true))
+      end
+    end
+
+    context "when value is smaller than the balance" do
+      it "returns true" do
+        balance = build(:balance, amount: 70.342)
+
+        expect(balance.withdrawal!(20)).to(eq(true))
+      end
+    end
+  end
 end
diff --git a/spec/models/fiat_balance_spec.rb b/spec/models/fiat_balance_spec.rb
index 704bfc1..957d7f1 100644
--- a/spec/models/fiat_balance_spec.rb
+++ b/spec/models/fiat_balance_spec.rb
@@ -25,4 +25,32 @@ RSpec.describe(FiatBalance, type: :model) do
   describe "associations" do
     it { is_expected.to(belong_to(:user)) }
   end
+
+  describe ".withdrwal!" do
+    context "when value is greater than the balance" do
+      it "raise ActiveRecord::RecordInvalid" do
+        balance = build(:fiat_balance, amount_cents: 100_00)
+
+        expect { balance.withdrawal!(100_50) }.to(
+          raise_error(ActiveRecord::RecordInvalid, "A validação falhou: Quantia saldo insuficiente")
+        )
+      end
+    end
+
+    context "when value is equals to the balance" do
+      it "returns true" do
+        balance = build(:fiat_balance, amount_cents: 100_00)
+
+        expect(balance.withdrawal!(100_00)).to(eq(true))
+      end
+    end
+
+    context "when value is smaller than the balance" do
+      it "returns true" do
+        balance = build(:fiat_balance, amount_cents: 100_00)
+
+        expect(balance.withdrawal!(90_00)).to(eq(true))
+      end
+    end
+  end
 end
diff --git a/spec/models/user_spec.rb b/spec/models/user_spec.rb
index ce70b21..bc8481d 100644
--- a/spec/models/user_spec.rb
+++ b/spec/models/user_spec.rb
@@ -31,7 +31,7 @@ RSpec.describe(User, type: :model) do
 
   describe "associations" do
     it { is_expected.to(have_many(:documents)) }
-    it { is_expected.to(have_one(:balance)) }
+    it { is_expected.to(have_many(:balances)) }
     it { is_expected.to(have_one(:fiat_balance)) }
   end
 end
diff --git a/spec/policies/balance_policy_spec.rb b/spec/policies/balance_policy_spec.rb
index eb3c421..158e99e 100644
--- a/spec/policies/balance_policy_spec.rb
+++ b/spec/policies/balance_policy_spec.rb
@@ -2,5 +2,41 @@
 require "rails_helper"
 
 RSpec.describe(BalancePolicy, type: :policy) do
-  pending "add some examples to (or delete) #{__FILE__}"
+  context "when user has balances" do
+    it "return only balances from a user" do
+      create(:balance)
+      create(:balance)
+
+      user = build(:user)
+      balance = create(:balance, user: user)
+
+      balances = BalancePolicy::Scope.new(user, Balance).resolve
+
+      expect(balances).to(eq([balance]))
+    end
+  end
+
+  context "when user has not balances" do
+    it "return empty array" do
+      create(:balance)
+      create(:balance)
+
+      user = build(:user)
+
+      balances = BalancePolicy::Scope.new(user, Balance).resolve
+
+      expect(balances).to(eq([]))
+    end
+  end
+
+  context "when user is nil" do
+    it "return empty array" do
+      create(:balance)
+      create(:balance)
+
+      balances = BalancePolicy::Scope.new(nil, Balance).resolve
+
+      expect(balances).to(eq([]))
+    end
+  end
 end
diff --git a/spec/policies/fiat_balance_policy_spec.rb b/spec/policies/fiat_balance_policy_spec.rb
index 9bf7e08..9fa3dce 100644
--- a/spec/policies/fiat_balance_policy_spec.rb
+++ b/spec/policies/fiat_balance_policy_spec.rb
@@ -2,5 +2,43 @@
 require "rails_helper"
 
 RSpec.describe(FiatBalancePolicy, type: :policy) do
-  pending "add some examples to (or delete) #{__FILE__}"
+  describe "::Scope" do
+    context "when user has balances" do
+      it "return only balances from a user" do
+        create(:fiat_balance)
+        create(:fiat_balance)
+
+        user = build(:user)
+        balance = create(:fiat_balance, user: user)
+
+        balances = FiatBalancePolicy::Scope.new(user, FiatBalance).resolve
+
+        expect(balances).to(eq([balance]))
+      end
+    end
+
+    context "when user has not balances" do
+      it "return empty array" do
+        create(:fiat_balance)
+        create(:fiat_balance)
+
+        user = build(:user)
+
+        balances = FiatBalancePolicy::Scope.new(user, FiatBalance).resolve
+
+        expect(balances).to(eq([]))
+      end
+    end
+
+    context "when user is nil" do
+      it "return empty array" do
+        create(:fiat_balance)
+        create(:fiat_balance)
+
+        balances = FiatBalancePolicy::Scope.new(nil, FiatBalance).resolve
+
+        expect(balances).to(eq([]))
+      end
+    end
+  end
 end