Revision control systems like Git are important for today's software ecosystems to help build better scientific software and improve developer productivity on a project. Here is an excellent article if you wish to understand Git Pull Requests.
|Article title||How to submit a pull request|
Pull requests allow contributors to tell others about the modifications and changes made by them to a certain Git repository. Pull Requests (also called Merge Requests in Gitlab environments) enable qualitatively different workflows than direct commits to a repository.
By explicitly requesting that a commit (a change to the repository content) be added to a repository, the effects of the commit can be reviewed, tested or refined and the commit eventually integrated or rejected, enabling better management of the repository quality and integrity. The article How to submit a pull request by Zell Liew provides a nice conceptual and step-by-step description of how to submit pull requests on GitHub.