To integrate it to the application,it offers 3 different integration methods.

1. Inline Checkout

In inline chekout,we displays a secure payment form as an overlay on your checkout page. .It collects the buyers's billing/shipping address and finalize the cart total sum
the function of inline checkout is same as standard checkout, but when the required parameter is missing(buyer's name,email address and billing address),it willredirect to the standard checkout.

To know about request parameters, and response please refer to https://www.2checkout.com/documentation/checkout/inline-checkout

2. Standard Checkout

It can handle every part of the buyer’s checkout process on a single page. You can customize the whole checkout process to your needs by passing user billing/shipping information details, currency details, language and checkout steps.

To know about request parameters, and response please refer to https://www.2checkout.com/documentation/checkout/standard-checkout

3. Payment Api

In payment api,we are taking the credit card information with a simple HTML form on our website, and use our 2co.js JavaScript library to convert the credit card information into a secure token. We're sending the secure token to your server and submit the transaction using 2checkout API.

a)create token:

Here we collect the payment details using a form(#myform) and generate a secure token 

b) create sale: after token has been created, you can use it to charge the customer through our server-side authorization API call.

# Setup credentials and environment

    twocheckout.Api.auth_credentials({

        'private_key': 'sandbox-private-key',

        'seller_id': 'sandbox-seller_id',

        'mode': 'sandbox'

    })

# Setup arguments for authorization request
    args = {
        'merchantOrderId': '123',
        'token': request.form["token"],
        'currency': 'USD',
        'total': '1.00',
        'billingAddr': {
            'name': 'Testing Tester',
            'addrLine1': '123 Test St',
            'city': 'Columbus',
            'state': 'OH',
            'zipCode': '43123',
            'country': 'USA',
            'email': 'example@micropyramid.com',
            'phoneNumber': '555-555-5555'
        }
    }

    # Make authorization request
    try:
        result = twocheckout.Charge.authorize(args)
        return result.responseMsg
    except TwocheckoutError as error:
        return error.msg

for more details refer  to https://www.2checkout.com/documentation/payment-api/

Return Process:

after successful transaction using 3 methods,we can redict to the website by giving the return url in the production account,or we can also mention in the form using the input field x_receipt_link_url=http://www.yoursite.com/return