It works just like it says! You order online, they will send you an email with your ticket(s) attached. Simply open the files, print them (make sure you have paper and ink). Make sure the bar codes print and don't smear, as they scan those to get in to the park.
You just get in line like it's a normal ticket. Skip the ticket booths. They will scan your 8 x 11 sheet of paper (and take it) and issue you a small, blue ticket like everyone else has. You then can use it for FastPass, etc.