How to do I use Paypal's Button Manager API?

[pipa_med]

I'm trying to add PayPal to my website so people can buy pictures I took. I would like the people to add whatever pictures they want in whatever quantity they want to a cart then check out. I've been scouring PayPal's website for the past two days and cannot figure out how to use the Button Manager API. It seems to tell me what I am capable of doing, which is why I'm thinking the Button Manager API is what I'm looking for. However I cannot find any instruction on how to implement it. I'm doing this with ASP.NET in C#. Are there any good guides available on how to use the Button Manager API?Thank you.