Hi, Jennifer! With very few exceptions, you can still order anything you want on the menu. There may be a special menu item, or items meant to be shared, which would be excluded from the plan, however, most restaurants allow you to use two credits for a meal meant for two guests. You would also need to use an extra credit for something like a pizza.
Some restaurants, like Les Chefs de France, offer a prix fixe menu that you can use your dining plan credits for. You are not required to purchase the prix fixe meals, but for some guests, it's a great option.
You can find everything you need to know about the dining plan by clicking
Walt Disney World Deluxe Dining Plan. Since you are familiar with the plan, you'll be able to compare the updates to the plan in 2013 with plans you've used in past visits.
Have a great upcoming vacation!