Good luck! You'll probably get a headset and will be (partly, since there's usually a couple on the ground floor returns team) responsible for taking items from behind the tills that belong to another floor, putting them on a rail or in a box (tote), and calling other floors' return teams to meet them in the back (mini-stock room) area to swap items so you give them their stuff, and they give you your stuff, and then putting the stuff you've received back out on your floor. It's a fast-paced and tricky job to get the hang of, but I'm sure you'll be well supported by other people on the returns team.
It's a different job to simply being responsible for a zone (or department), which mainly consists of keeping the zone tidy and fetching stock.
I should finish by saying I've only been working at my store for over a month but I'm genuinely really enjoying it! The people are great and the job really is the right level of pace.