You use it just like a credit card. Just don't forget to call or go online & transfer the reward points to a Rewards Card. They mail you a plastic Rewards Card which looks just like a credit card, and it is swiped anywhere (almost) in WDW or at the Disney Resorts. You can even call ahead & pay for your room with the numbers on the card.
If you're going to use it to pay against your room or purchases made & charged to your room, I'd have them swipe the Disney Rewards card 1st, use up those points, then pay the balance on another CC (or by check, however you plan to do it. ), at check-out. We did this at AKL in '06 - you have to give them a regular CC to have on file as well as the Rewards Card, but everything was "paid for" at the end at check-out, not every day as we charged to the room. I don't know if that makes sense to you, or if that's even what you're asking. Hopefully it helps!