You want to create a new branch named edit-mobile-locations based on develop
branch. In the future you want to push the branch commits to bartsimpson
remote repository.
The first step is to checkout the base branch:
git checkout develop
Now you can create a new branch based on the current one:
git checkout -b edit-mobile-locations
Since you have been used checkout command, your working tree is pointing to
the new branch.
More about checkout in git-checkout Manual Page