Work with freelancer on one project


I have a project, which I worked on alone until now. So I also have just worked in the master branch.
Now I’m letting a little part code by a freelancer. I’,m asking myself on how to safely let him work on mit Gitlab Project.
First of all I would create a branch for him on which he works. Also I would create a branch for myself in which I can code parallel.
Now two questions:

  • How can I be sure he doesn’t edit/delete other branches than his own branch?
  • Or there other things I have to pay attention to?