If you forked someone’s repository (forked, explained under terminology, scroll up) then follow these instructions Fork A Repo - Github Help and then the commands below.

If you are the upstream yourself, (i.e. you are the guy who created the original repository) then follow the instructions below

• $ git clone <add the repository address here along with .git at the end> (clones/copies everything from that repository to your local machine)
• $ git add filename.extension (this adds the file you want to change on the server)
• $ git commit (this commits your changes to the repository with an explanation message)

• $ git push origin master (this finally sends all your changes to the server. This is the final step of changing the code on your repository on the server)

  You just started using GitHub. Congratulations :D