How to create a Payment Gateway in asp.net (Demo)

Question

Hi all,

 

I want to create a payment gateway for my degree as a demo. 

I have no idea how to do it. I tred  it through Paypal services (sandbox).But when i logged into paypal account and created a account.after went to sand box t doedn't show me marchant  account or any thing.

 

If some one can tell me how to create payment gateway step by step it would be much thankfull to you.

 

Thank you n advance.