what do you do or what are they for; sitter treats?

Everyone here starts out with 1 treat. That is for registering on this board. It means nothing, Participants receive additional treats (which get you nothing) for asking good questions or providing good answers. The purpose behind the "treats" is explained in the FAQ linked at the top of the page.

You would do better if you are having problems registering with Rover to call customer support at [Edit: Rover’s contact options have changed. Visit the Rover Help Center at https://support.rover.com/ to find the phone number, help articles, or chat with the team].