using_paypal_gem.md

-> Add 'gem activemerchant' in gem file
-> bundle install
-> Go to "developer.paypal.com" and create an account(also known as Merchant Account) with US address details.
-> It will create two dummy test account for buyer and seller(alias facilitator) in "sandbox.paypal.com".
Ex:
    Seller account  --->  naveengoud-facilitator@gmail.com   Buyer account  --->  naveengoud-buyer@gmail.com
To see test accounts details Click on "Dashboard -> Accounts"
Now set the password for both test accounts by clicking on profile link

Go to seller account(i.e, facilitator) profile details and copy the API Credentials i.e, Username, password and signature
Ex:     Username:  naveengoud-facilitator_api1.gamil.com       Password:   VSPALJ5ALA5YY9YJ     Signature:   AVLslxW5UGzEpaDPEK4Oril7Xo4IAYjdWHD25HhS8a8kqPYO4FjFhd6A   Set these API Credentials in "config/environments/development.rb" as follows, add the below code with API credentials

  config.after_initialize do  
ActiveMerchant::Billing::Base.mode = :test         
        ::GATEWAY = ActiveMerchant::Billing::PaypalGateway.new(  
             login: "merchant_api1.gotealeaf.com",  
            password: "2PWPEUKZXAYE7ZHR",  
            signature: "AFcWxV21C7fd0v3bYYYRCpSSRl31A-dRI5VpyF4A9emruhNYzlM8poc0")  
end

From here onward follow the Rails cast 145 episode (http://railscasts.com/episodes/145-integrating-active-merchant)