When you get to parks and characters there are people there willing to take pictures of you and your family. They then put your photos on a plastic card-- photo pass card -- then when you go to the next photo stop you give them the card and they add on that session and so on and so on. Then when you get home you can view your photos and order photos as well as every photo on CD (with the rights to print them), a video, a book and some other stuff.
Always remember to write down your photo pass number or take a picture of the back of your PP card with your camera so that if you lose the card you don't lose the pictures.