Publishing allows editors to merge changes from one branch to another. Choose to merge directly or with a pull request. Selecting a publish branch enables the publish interface for your site. This is useful for staging sites.
To connect a publish branch and enable publishing:
Go to Site Settings / Publishing and click Add Publish Branch.
Select the branch you want to merge into and click Use Branch. This fails if there is no additional branch in the repository.
All editors have access to the Publish section in the sidebar. Clicking Publish attempts to merge into the publish branch. Pending changes are also displayed in this section.