An ADR is an Advanced Dining Reservation. I know there are vets out there who will correct me if I am wrong, but you can make reservations starting 180 days out from your trip.
Lastly, FastPass is a tool that Disney implemented on their more popular rides. You can walk up to a kiosk and print one. You need to swipe your ticket, and it will print out a time (a one hour range) to come back to that ride. When you come back, you can enter the FastPass line instead of the regular line. You can only print one FastPass out at a time. When your FastPass expires you can go to another FP kiosk and print out a new one.