When you enter each of the parks, you will see 'professional' photographers standing there, asking if anyone wants a photo taken. You will also find these photographers around the parks and at some of the character meet/greets. If you choose to have a photo taken, they will give a credit card type card, which you will then use for all photos taken by the pro's at WDW. Each time you have a photo taken, the photographer will swipe your card. Then, you can view them several different ways. I always wait until I get home, log onto the PhotoPass site and enter the number on the back of the card. This will up all the photos you had done while in WDW, then you can order any you may want. You can also view them in the parks before you go home.
I have been using the same photopass card for 4 trips now...love the service. Yes, it can be a bit pricey but it's better than lugging the photos home. Test Track now has their attraction photo set up on photopass...other attractions will be following suit down the road.
Hope this helps...if not, ask away!