Tipping is standard practice at table service restaurants in the US. Table service restaurants are those where you sit down and a waiter/waitress brings you a menu and then your food. At Walt Disney World, this also includes buffet-style restaurants, where the server explains the buffet items and brings your beverages to the table.
The standard tip in the United States is between 15% and 20%, depending on your satisfaction and level of service. At WDW, a tip of 18% will be automatically assess for groups of six or more people. If you have a group of fewer than six people, then you can choose the amount to tip, but again, anywhere between 15%-20% is acceptable.
You can read more about this in the post
HERE.
When you're on the Disney Dining Plan, your tip should be based on the amount that your food would have cost if you were paying for it out-of-pocket. This amount will be totalled on the receipt you will receive at the end of your meal.
Enjoy your visit to Walt Disney World