Integrate instamojo api in rails app

I am learning payment gateway integration in rails. I chose insta mojo and was working but the documentation they provide is very inconvenient and hard to understand..

http://ift.tt/2AAdASd

I have no idea where to Set my API keys

require 'Instamojo-rb'
api = Instamojo::API.new do |app|
  app.api_key = "api_key-you-received-from-api@instamojo.com"
  app.auth_token = "auth_token-you-received-from-api@instamojo.com"
end` 

I tried instamojo.rb in initializers and tries to run console but it gives error that no such method exists.