For those that are using UI to branch click Right Mouse on repository then Tortoise Git -> Create Branch...

https://s3-us-west-2.amazonaws.com/secure.notion-static.com/769e2977-1f4b-4e03-a47f-5fbe5dcd1c75/Untitled.png

New window will open -> Give branch a name -> Tick the box Switch to new branch (Chances are you want to start working with it after branching). -> Click OK and you should be done.

https://s3-us-west-2.amazonaws.com/secure.notion-static.com/8fb5113a-626f-4590-8c37-ba7a52a31ac9/Untitled.png