If you are on the regular dining plan (1 TS, 1 QS, 1 Snack) it does not include an appetizer. There are a few exceptions where you will get an appetizer - CRT and Akershus at lunch and dinner, Fantasmic and Candlelight Processional Dining Packages, the 3 dinner shows, and if you order the prix fixe menu at the few restaurants that have one (e,g Chefs, Restaurant Marrakesh, Monsieur Paul, although the latter 2 have an upcharge.)
If you have the Deluxe Dining Plan it includes an appetizer per adult at lunch and dinner.