Setting the default branch→
The default branch is considered the base branch in your repository, against which all pull requests and code commits are automatically made, unless you specify a different branch.
Viewing branches in your repository→
Branches are central to collaboration on GitHub, and the best way to view them is the branches page.
Deleting and restoring branches in a pull request→
If you have write access in a repository, you can delete branches that are associated with closed or merged pull requests. You cannot delete branches that are associated with open pull requests.