Dream Fastpasses are part of the Year of a Million Dreams promotion, and you can only get them if you happen to be where they are being distributed at the right time. If you are lucky enough to get one, you will receive a plastic card with tear-off tabs of the most popular attractions in that particular park (for example, Everest, Dinosaur, Kali River Rapids and Kilimanjaro Safaris are included on AK's dream fastpass). You may use each tab only once to ride in the fastpass line (gets you into the ride quicker), but the pass itself is good for the entire day (ex. You can only use the fastpass for Everest once, but you can use it at 9am, and not use any others until 4pm and still be fine).
Regular fastpasses are available at select attractions. You insert your park ticket into the machine and receive a ticket valid for an hour at a certain time of day (For instance, at Splash Mountain, you put your ticket in at 10am. The Fastpass ticket might say to return between 1 and 2pm. Between those times, you can get into the fastpass line). You can't get another fastpass until the time on the first pass has already started.
Hope that helps! Have a great trip!