We have APs for several years. The CMs will tell you that if you are going to be at WDW more than 7 days in one year, that you would be better off buying an AP.
The way they work is that you can buy the ticket anytime before you go, or when you get there. If you purchase before you go, either at
Disney store or online, you will get a voucher for the tickets. When you arrive at the park the first day, you will have to go a ticket counter to get the actual passes.
The timer on the tickets does not activate until the first time you use them. Then they are good for 365 days after that date. So, if you plan your trips carefully, it is easy to get more than one trip per ticket. If you decide you love them and want to renew the next year, however, the anniversary date stays as the first time you used the ticket.
The ticket does come with some special discounts, etc. These usually include special room rates as well. However, they are not enough to justify spending the money if you are only on a short trip and do not plan to return within a year! Also, there are several times when they have special passholder events. My experience with these is that they are usually PACKED!!
You can view the actual rates on the disney website. We will be buying one for my MIL, even though she probably won't be visiting again within a year. We will be staying for eight days, and financially, this ticket is the cheapest for that long of a stay.
Have a great trip!!