How to I implement stuff like Payment system, facebook user info and the like? (Pls help me.)

Hi there guys, good vibes. I'm a beginner/intermediate php/Mysql programmer and I can confidently say that I am good with all the data driven stuff (including ajax). So now that im over the 'basics', I want to know where to start when it comes to learning more difficult stuff like Facebook user info inclusion, payment processing, rich text editors and the like.

When I read the documentation of these packages, I come across vague references to 'access tokens', 'app id/secret' and the like. All of which I really do not understand. My problem is that there isn't any straight forward concise tutorials out there that explain these things in details.

So i'b be glad if you can give me some general guidelines of how to proceed. Thanks