What is a collaborator?
If you want to collaborate with another user on a list, you can add that user's email to your list. Your collaborator can then add their items to your list and reorder all of the items added to that list.
The collaborator can not edit the list details or mark you items as Got it.
You can not mark the collaborator's items as Got it.
Currently it's only possible to add 1 collaborator.