Hi, Andrea!
No worries!
When you check in to your Walt Disney World Resort hotel, you'll be advised of all of the entitlements on your
Disney Dining Plan. This will include a printout of your total number of snack and meal entitlements; you'll then be able to take your Key to the World Card over to the dining location of your resort, where you can pick up your Resort Refillable Mugs (1 per person on the Dining Plan.)
That mug will save you lots of time and money by enabling you fill up at any fountain location at your resort. Then, when your vacation is over, you'll think of all of the wonderful moments you enjoyed each time to use it at home. (These are my favorite travel mugs, and because they are capped, our younger child is allowed to enjoy some hot chocolate while snuggling in on the sofa on a chilly day.)
Take a look at the link above, and send me another question which includes which Dining Plan you've chosen. I'd be happy to walk you through your entitlements, how best to use them as well as suggest locations for your family's favorite meals. (It's so much fun helping a new Guest learn how to pack the most pixie dust into an upcoming trip. I love it!)