You need to install msysgit first, Peopleperson49
After that you need to fork from master repo to make your own fork repo, from there you can change the files on your local disk and later you can commit & push to your fork repo.
When you feel that your commits are done, then you can make a Pull Request into the master repo
Just be sure to Pull/Fetch before you edit the files on your local, because if you forgot to do that, there's a chance that your commit will got conflicted with the current branch