# Once a repo is cloned, you'll be working inside of the default branch (the default is `master`)
git clone https://github.com/<git-user>/<repo-name> && cd <repo-name>
# make changes and stage your files (repeat the `git add` command for each file, or use `git add .` to stage all)
git add <filename>
# now commit your code
git commit -m "added some changes to my repo!"
# push changes in `master` branch to github
git push origin master