If you try to edit a file from a repo you can read, but not write-to, from the GitHub interface, it will fork the repo, make a branch for the edit, then send a

If you try to edit a file from a repo you can read, but not write-to, from the GitHub interface, it will fork the repo, make a branch for the edit, then send a PR from that branch. If you try this again in the future, you'll get a different branch. It is possible to update a fork from the GitHub interface... you make a new pull request from the original tree to your fork, then accept that PR. If you just hit "Pull Request" when looking at your fork, you'll see a "reverse bases" link that will do this.