In general, you put your ticket into the fastpass machine at selected attractions, it gives you your ticket back and a pass that tells you what time to return. At the time indicated, you can return to the fastpass entrance and bypass the standby line. You can't get another fastpass until, I believe, the time on the one you hold comes up, unless you get a fastpass that a CM passed out to you without going through the machine, which occassionally happens.