Hi Corey,
Thanks for visiting the Disney Parks Moms Panel! The Disney Dining Plan can be confusing, especially if it's your first time visiting.
This page provides an
overview of the dining plan. There are several plans offered - most people find the standard plan, which offers one snack, one quick service, and one table service meal credit per person per day, to be the most beneficial. You can use the credits in any order over your trip, so for instance, you can have two table service meals one day and none the next. When we have the Disney dining plan, we do sometimes end up purchasing food in addition to the plan.
Most of the restaurants do participate in the plan. This
PDF on the Walt Disney website provides a listing of participating restaurants (on page 3).
Keep in mind that if you are planning to dine at table service restaurants, I'd highly recommend making advance dining reservations.
I hope that helps! Have a great vacation!