The payment method model, code etc are defined in the this file. This is first important step.
This is required to create the system configuration part of payment method
3. Model class
Create a model class for the payment method which should extend ‘payment/method_abstract’ class.
define here the operation of payment method like authorize, capture etc
Above are the important classes, optional things
1. Form Block getFormBlockType()
This return a block type, which is used to render a form shown in the checkout page. e.g credit card forms etc
2. Info Block getInfoBlockType()
This is used to display payment information in the checkout progress block
there are many other functions like
getOrderPlaceRedirectUrl(), assignData(), prepareSave(), isAvailable(), refund(), void()