This is done using GitHub Issues.
Use issues to track ideas, enhancements, tasks, or bugs for work on GitHub.
For more information on issues see:
This is done using GitHub Pull Requests.
Pull requests let you tell others about changes you've pushed to a repository on GitHub. Once a pull request is opened, you can discuss and review the potential changes with collaborators and add follow-up commits before the changes are merged into the repository.
For more information on Pull Requests see: