Creating a copy of a remote repository you don’t control to a remote repository you do control. The forked relationship allows you make changes to your remote repo and suggest them as changes to the remote repo you don’t control.
A new branch is a copy of an existing branch with the full set of files, and history. Changes can be made to files and new commits can be added without altering the files or history of the original branch.
This gives you the ability to add new work in a safe environment.