Just to clarify, rocketman and spideyhulk are talking about different kinds of express.
The express Rocketman was referring to is the free Express. It's very similar to Disney's fastpass in that you scan your admission ticket and in the machines around the park and you can get a pass. If you dont like the offered times, you can simply CANCEL and nothing is put on your ticket. Otherwise, you choose your time and a pass will print out with your return time. The computer will also tell you when you can get your next Express pass (generally 1-2 hrs after you got that one).
Spideyhulk is referring to Express plus. This you pay for, up to $25 per person, but you get a pass that's good for the whole day, one express access per attraction in whichever park the pass is issued for. They are park and date specific, so you can't use Studio Express Plus in IOA...