They give each person in your party a card to put in the fast pass machine and it spits out a fast pass that is for the current time. Each person in your party (including children) gets one and each card can be used 4 times. The are good for two or three days.
We did it last year because we were interested in learning more about the DVC. The younger kids stayed in the kid's club and played while dh and oldest dd and I went through the presentation.
The fast passes were a nice bonus and different than the fast pass in the park