If you place a credit card on file, you may charge things back to your room using your room key. Value resorts have a $500 limit, Moderates have a $1,000 limit, and Deluxes have a $1,500 limit. Once you reach this limit, your credit card on file will be automatically charged that night, and you will recieve a new limit. Any charges at the end of your stay will be billed at 3am of the morning of departure.
If you wish to pay in cash instead of having it charged to your card, you can give cash at check-in, and they will take away from the cash instead of charging your credit card. (Once you run out of cash, then it goes into the resort credit limit as described above)
Or, you can pay the night before departure. If you wait till the day of departure, your card will have already been charged.
Due to credit card companies (this is all over, not just Disney) it can sometimes take 2-3 billing cycles before a credit appears on your credit card. I don't know why, but that's just how they work.