You have to add a MYW Package with dining in order to get dining. So you get your room, at least a one-day MYW ticket, and the dining plan. You call the reservation line, I think it's (407)wdw-7785.
Free dining is in late August till mid-Sept. You book a MYW package which includes room and at least a one-day MYW ticket then you will get the free DDP added on.
Hope this helps!!