How to work (checkout) on more than one GIT branch at a time?

I'm using GIT and have many branches and need to work on several simultaneously, specifically files in one branch are not in another, and constantly having to

• check out branch a
• work on it
• make a commit
  
  
• check out branch b
• work on it
• make a commit
  
  
• recheck out branch a
• work on it
• make an updated commit (to revise the first commit and avoid hundreds of intermediate commits)
  
  
• etc.

is becoming very tiresome.

Surely there's a smarter way to work on more than one branch at a time?

I read that git has a worktree feature that supposedly helps. I read here:

https://blog.jetbrains.com/idea/2016/02/intellij-idea-16-eap-improves-debugger-and-adds-git-worktree-support/

worktrees are supported, but I can't find anything in the PHPStorm documentation, forums or knowledge base on how to use GIT worktrees and/or how to work on more than one branch at a time.

Thanks