Two scenarios for starting to work on a feature branch. If the feature branch is yet to be created you can create it locally and push it to the remote repository creating a new branch.
New branches can also be created from the GitLab gui, or it may have already been created by someone else via a Push. In this case you can pull the remote branch into your local repository and use checkout to create a local feature branch that will track it's remote mirror. Two options provided.
You may also set up your local repository by cloning the remote repository, steps to do so are also listed.
For pushing, your local feature branch should have the same name as the corresponding remote feature branch.
Before switching or checking out branches ensure changes made on current branch are either committed or stashed before switching.