Hello Yorth!
Depending on which type of Dining Plan you have, this may or may not be correct.
If you are on the "basic" Dining Plan (which I use all of the time), you are entitled to one non-alcoholic beverage, one entree and one dessert at each Table Service location which is NOT considered "Signature Dining." At a Signature Dining Location (The Hollywood Brown Derby, for example) a meal will cost you two Table-Service entitlements. On the other hand, if you are on the Deluxe, Premium or Platinum Dining Plans, you are also entitled to an appetizer at lunch or dinner.
If you are on the "basic" Dining Plan, then, and book your Table-Service reservation at a Walt Disney World restaurant which participates in the Dining Plan and is not considered a Signature Dining location. When you order, you may order any entree, no matter what the cost, and it will be included in your plan at no additional cost. (This is why, with careful planning, you can really save a lot of $ by being on the plan. We try to reserve a table at the more expensive, single Table-Service entitlement restaurants, then order the most expensive entree on the menu that we like, which is usually an item that would normally be out of our price range.) Should you wish to order an appetizer or a glass of wine, you can do so, but you will be charged for those.
Again, if you are on the "basic" Dining Plan, you can also dine at a Signature Restaurant, which will "cost" you two Table-Service entitlements, and order in the same fashion. Take a look at the various
Dining Plan PDFs for a list of how the plans differ from one another.
I hope this helps to clarify the Dining Plan for you! Please send more questions as you think of them; I love to help advise folks about the best use of their Dining Plans as well as other details of their magical Walt Disney World vacations! :-)