To use git:
1. Make a repository on github
2. Open a terminal, decide which directory you want the repository
$ git clone https://github.com/username/username.github.io
$ cd username.github.io
Modify the repository how you wish. When you're ready to push it to github:
$ git add --all
$ git commit -m "Some message describing the update"
$ git push -u origin master
That's it!