Paypal payment work

I have a web-application in asp.net framework (C#) which currently accepts payment using Paypal i.e. I have a business account with paypal. However, I want to implement a wallet based system in my website using Paypal button. That means I will have to allow the customer to recharge money in their web-wallet based on their payment using paypal button. But I don't know how to get the data of the successful payment amount from paypal to be sent to my web-application so that same can be updated using code in the web-application. I need someone who can do this