There are two buses that take you to the airport. One picks you up at the main entrance (in front of OC1). DO NOT TAKE this one, because it'll take you to the loooooooong way around the airport, stopping at Tech Ops and cargo, before going to the terminal building.

The other bus picks up in the parking lot in the back. If you walk past the museum, you'll see a fence with an opening and the bus stop. That bus runs more frequently and goes straight to the terminal building.