Hello,
I read lots of tutorials and so on, but because I am from Germany I am not so good in English, I understand nothing. And now I want to add my own economy API, my problem now is that I don't know how and I don't know how GitHub work.

So is there a way that you can do it for me?

I'm sorry, I don't have the time to walk someone through development/git process and getting everything setup. I also don't know german, I'm a native english speaker so attempting to communicate technical information is going to have the same barriers as tutorials.

The best I can really do is just point you to some resources. You'll need to be able to do basic java development with the bukkit API, and handling of dependencies yourself. you could ask on bukkit/spigot forums for help with getting setup and developing if there's something you're missing.