Hi Dara!
Some guests save a lot of money by using a Dining Plan. Other guests don't save as much and some actually spend more by being on a Dining Plan. You can get more information on the various plans
here. If you are not sure about the Dining Plan, then I suggest looking at the standard Dining Plan and the Quick Service Dining Plan.
In a nutshell, the standard Dining Plan provides 1 Quick Service meal, 1 Table Service (full service) meal, and 1 snack per night of your stay at Walt Disney World. The Quick Service Dining Plan provides 2 Quick Service meals and 2 snacks per night of your stay. Not all restaurants participate, but most do; you can see a list of participating restaurants in the brochures available on the web page.
I suggest looking at the menus for the various Quick Service and Table Service restaurants at the independent website AllEars.Net. They do a very good job of keeping their menus up to date. You can then compare the cost of being on the Dining Plan to not being on it.
Regardless of whether you are on a plan or not, however, I suggest making an Advanced Dining Reservation (ADR) for any Table Service restaurants you are interested in. ADRs can be made up to 180 days in advance. Many restaurants book up very quickly.
Have a magical vacation!