Something confused in payment extension app.

[Matthew Shawn]

When I write the payment apps , should I just over write the checkout method in custom payment app ?   I look up the docs of paypal payment and amazon payment app, but I can't understand , and do here also need a migration.py for create new table for save third payment parameters?

I have read <learning python 5th> and <web development with Django Cookbook> ,but I can't find out the inherit relation between Django and Oscar, and don't know how to write Oscan extension apps. Do I read the right books?