git branch <branchname>
Copy current branch as a new branch
git branch creates a new branch with the name you specify. However, it doesn't switch you to that branch; it only creates it. To switch to your new branch, you would use git checkout.
If you want to create a new branch and switch to it at the same time, you can use:
git checkout -b <branchname>
Specific examples:
git branch refactor-homepage