The only restaurant you need reservations for is Emeril's. (407) 224-2424
Priority seating is taken in advance as a convenience (407) 224-9255. Also as you exit the parking area, there is a kiosk where you can make same day and advance priority seating. Note some restaurants won't take priority seating between 6pm and 8pm.
If you want to dine at the on-site hotels call (407) 503-DINE. Every one is invited to dine at the hotels and the short water taxi ride (free) from Citywalk makes it convenient.
If you are on-site hotel guest, just show your room key and you will get next available table.