Book by 8/20. If you were traveling between 8/21 and 10/4. You had to buy a package(resort stay and tickets) and stay at least 3 nights, dining would have been included for free. They still sell the dining plan at $35 for adults & children 10+ and $10 for children 3-9 per night you stay.
DDE is Disney's Dining Experiece which is a card you can buy if you are an AP holder or a FL resident. It gives you 20% off at selected Disney restaurants.