Hi, Elizabeth! The AAA Diamond Parking is only available during certain times, and in order to gain access to this preferred parking lot, you have to purchase certain vacation components through AAA. You can get the pass with some of the AAA Walt Disney World vacation packages, and in some cases, you can get the parking pass with ticket purchases.
You do still pay the regular parking fee when you arrive at the theme park, however, the Diamond Parking is usually fairly close to the front of the parking lots. If you have the parking pass, you will be directed by the Cast Members attending the parking lot where to go.
The Diamond Parking pass will be mailed to you with your vacation documentation or your passes when purchased through AAA. You can contact your local AAA office to get more information regarding the pass and other AAA vacation package information.
I hope you enjoy a wonderful Walt Disney World vacation!