Chrissy72,
To get Annual Pass (AP) rates you need to have an annual pass at check in. The reservation can be made without the pass, when AP discounts are available. The annual pass is usually cost effective when you are going to the parks for 8 or more nights in one year, or when the discount exceeds the additional cost of the AP. We usually end up making two trips on the pass which makes the second trip a bargain. The AP also has the advantage of not feeling like you are wasting a pass day when you only spend a few hours at the park in a day.