how to develop web app to sell online [closed]

Question

I have made a booking system for online ticket reservations, but they cant pay online! so I now I have a client that he wants me to make them able to pay tickets online.

The problem is that I have never worked with ecommerce before. Is there any good book or tutorial how to start with developing for banks? because my client is going to choose the bank that will give me the gateway to make the transactions.

What is the first thing to do? are there any instructions from the bank, how to setup the gateway? or they will help me? or I must know all this by myself? what are your recommendations?