This extremely condensed tutorial shows the steps for creating a Pull Request on GitHub.

1. Press the Fork button on the repository you want to make a PR for:
   
2. Clone your fork using git clone https://github.com/[your user]/therepository --depth=1
   
3. Create a new branch for your changes using git checkout -b new_branch. You can name the branch whatever you want, but you'll need this name for future commands
4. Make your changes and commit them on the new branch.
5. Push your changes to your new branch with git push --set-upstream origin new_branch
6. Go to your repository on GitHub, and press the Compare & Pull Request button
   
7. Describe your changes, then press Create Pull Request
   
8. If the maintainers approve your change, then you'll be prompted to delete your branch / fork, which you can optionally do.
   

Congratulations, you've created a Pull Request on GitHub!