- You fork the original repository. This creates a copy of that repository under your own account
- Clone that repository (the fork) to your local PC, either with the git commandline, or the Github for Windows client
- Make the required changes locally
- Use your client of choice to commit these changes
- Once done, push the changes back to Gitnub
Once done to to your github repository with your browser. You'll see in the button bar, next to the branch button, a new button "new pull request", give it a description, and send the pull request back.