ok so for me this is kinda how it works:
1. create a fork of the fa repo (you can also save it to your pc as a repo and use it as your own copy, ect. i can explain about that separately.)
2. put your changes into your branch, make it all how you want, ect. make sure you change the right branch (the one you want your pull requst to go to) ask icedreamer which branch.
3. go to here: https://github.com/FAForever/fa/compare
4. press compare across forks
5. select your fork and branch, and compare it to the fa branch you want to pull request into
6. create pull request.
7. hope for the best