This was one of the greatest experiences of my life. This past summer I went to Ft. Benning to attend the US Army Airborne School for 3 weeks. It consists of 3 phases, one per week. Ground week is mainly learning how to wear the equipment and how to land without injuring yourself. You do more PLF's (parachute landing fall) than you'd like, but it keeps you from injuring yourself. Tower week teaches you how to act once you've exited the aircraft and are floating towards the ground. You practice "slipping" or steering the parachute away from other jumpers in the air and hazards on the ground. Jump week is the real deal. You jump from a C-130 or C-17 cargo plane 5 times. If you get scared when it comes your turn, don't worry because if you need help getting out the door, Sergeant Airborne (the instructor) will be right there as the jumpmaster to put a boot up your 4th point of contact. The "black hats" or instructors at Airborne School make sure you know what you're doing before they let you go up and jump.
Here is a video of an actual jump. Video It's extremely worth the wait for it to download. The external view of the door is exactly what you see as you exit (if you keep your eyes open) except just watching the video doesn't let you experience the prop blast or the few seconds of free fall. Absolutely incredible. Go to Airborne School if you ever get the chance!