this command copies the entire repo into a new tree that will appear as a sub dir. then you can explore that shit as you want knowing that the original tree is untouched.
example, I am at branch A and I want to check something at branch master:
git worktree add testTree master
the result of the above commands will be the creation of a new copy of your repo into a sub directory called testTree where the branch will be master. then we
cd into that directory,
after finishing our work we can easily delete the sub directory:
git worktree remove testTree