Hi Tina!
The Deluxe Dining Plan is a great option! 3 full meals, and most Disney restaurants come with an abundance of food, so bring your appetite (smile)!
You are correct that you would only see a charge if you don't show up.
Giving your credit card information during reservations basically serves two purposes:
1) To secure the reservation.
2) A source of payment for missed reservations, or reservations cancelled less than 48 hours from the designated time.
Generally what happens is you book now with your credit card and get a confirmation number. When you arrive at your resort, you will be giving a "Key to the World" card. This card is used for getting into your resort room, theme parks (if you purchased tickets), and last but not least your dining plan.
When you get to your table service, just show them your key card vs, pulling out a credit card. They will then use your key card for payment and return it with your remaining dining credits.
Good luck on your planning!