There is also a Video Walkthrough of how to do this if you prefer to learn over video.
Find the file you want to edit. Click the pen tool on the top right of the file to edit it. If you want to add a file, click "Add File". Click "Create new branch". Learn More
Make your changes. When you are ready, click Pull Request on the bar above the file. Then create
New Pull Requestand choose to set the request to merge to the
TechArch:mainbranch. Put any information you want to describe your changes on in the description, and you're done! Learn More.