Pull Requests are used to merge changes from a branch or remix back into the parent. They are a way to propose changes to a val, and they are the primary way to collaborate on vals with other users.
To make a PR, create a remix of the parent val, then visit the parent val’s Pull requests page where you will see an “Open pull request” button. If you’re the owner of the parent val, you can also create a PR from a branch of that val.