Help Needed in Learning Payement Gateway paypal, ccavenue, pay2u

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ASP.NET

PHP

PayPal

payment

Hello Friend,

I am developing website from last 6 months in
ASP.net and PHP .

Now i am getting requirement for making "ECOMMERCE" website with Payement Gateway paypal, ccavenue, pay2u etc..

but i don't know anything about payment gateway.

even i don't know how to implement it.

so can anybody help me to find the proper content from where i can learn a to z
about payment gateway.

It is related to payment and therefore i am asking here as i know that i will get the solution for my problem.

so any kind of material , books , videos , project anything if you have please guide me to it so that i can learn from it.

Thanks in advance.

Thanks & Regards.
Devendra Sarang.