Hi Sheri!
You get meals for each night of your vacation, so, for example if you are on the Disney Dining Plan staying 3 nights you will get 1 table service, 1 quick service and 1 snack for each night of your vacation, so you total (for one person) would be 3 table service, 3 quick service, and 3 snacks. These credits are given to you in bulk, so one you check in you have access to the credits and can use them however you like.
For example (keep in mind this will also vary with your arrival/departure) time as well. :
Day 1
Check in at hotel at 4 pm, eat Table Service dinner
Day 2
Quick service breakfast at resort, snack for lunch, table service dinner
Day 3
snack for breakfast, table service lunch, quick service dinner
Day 4
You'll have one quick service credit remaining for this day, and one snack credit
Depending on your check out time you might lack a meal or snack, but for the most part we make it work. Our last meal is typically eaten at the airport before we depart.
Your credits are good until midnight of your check out day, so keep that in mind as well!
Have a magical vacation!
Amanda