Check out Microsoft Docs for more information on configuring branch policies, at https://docs.microsoft.com/en-us/azure/devops/repos/git/branch-policies?view=azure-devops.
There's also some good information on other things you'll need to know when it comes to managing your branches. You can read all about that at https://docs.microsoft.com/en-us/azure/devops/repos/git/manage-your-branches?view=azure-devops.