Set API key in rails website

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("c51766be718d7d5e5a5aeff00b83e202"
    , "0e268600acb0b7ea8b8414007f5f9fee"
    , "http://ift.tt/2hpZLkz")

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