In simple Words, Pull requests let you tell others about changes you've pushed to a GitHub repository. Once a pull request is sent, interested parties can review the set of changes, discuss potential modifications, and even push follow-up commits if necessary.

Example:
Imagine that you built your work on your master branch on top of the v1.0 release, and want it to be integrated to the project. First you push that change to your public repository for others to see:

git push https://git.ko.xz/project master
Then, you run this command:

git request-pull v1.0 https://git.ko.xz/project master
which will produce a request to the upstream, summarizing the changes between the v1.0 release and your master, to pull it from your public repository.

If you pushed your change to a branch whose name is different from the one you have locally, e.g.

git push https://git.ko.xz/project master:for-linus
then you can ask that to be pulled with

git request-pull v1.0 https://git.ko.xz/project master:for-linus