EDIT: I added a couple of new pictures, as the ones before were cruddy and i can snowboard better now! YAY!
Step 1: !WARNING!
I AM NOT RESPONSIBLE FOR ANY DAMAGE YOU MIGHT INFLICT ON YOURSELF WHILE LEARNING THIS, SO DON'T SUE ME IF YOU DO.
Step 2: What You Need...
2. bindings! make sure the screws attaching them to the snowboard are tight before you start. You don't wanna be in mid-jump and realise that your bindings have fallen clean off your snowboard. Trust me, this happened to me while i was going down a mild slope and it HURT.
3. snowboard boots. another no brainer.
4.proper clothing. doing indies in shorts and a t-shirt will not only make you very cold, but it will also make you very painful when you wipe out (for those who haven't tried falling onto snow while moving while not covering all that vulnerable bare skin, don't try. i beg of you.)
5. (optional) snowboard protectors. they really do help. even though i nailed myfirst indy the first try, the second attempt wasn't that great. If I hadn't had my*trusty* butt protector, my tailbone woulda died. also, wrist protectors would help if you plan on breaking your fall with them after you wipe out (which you probably will)
6. a hill/mountain/snowpark/whatever can function like one of the above
7. a nice jump, preferably not very steep, maybe half a meter tall, DO NOT GO FOR THOSE THAT ARE MADE TO GO FOR ALTITUDE! You'd probably just kill yourself. Like i did. *note* then again, if you feel comfortable with that, go ahead. i just went on one that sorta flung me up into the air and it was fine...but really, you don't want to go off one that will hurl you 4 meters up into the air.
Step 3: ZE START
Step 4: Before the Jump
Step 5: ZE JUMP!
When you're ready, get up, and ride down to the jump. Try aiming as much as you can for the center of the jump, so you're not in danger of flying off to the side or falling of the side and killing yourself (again). Work up as much speed as possible by riding flat on your board and not turning. As you approach the jump, crouch down.
Then, as you get on the lip of the jump,...well...jump! Push off as hard as you can and fly. As you jump, grab your snowboard (There's a picture of what the different grabs are, but I suggest you start with an indy. this is probably the easiest grab you can do. An indy is when you grab the board just in front of your back binding on your toeside with your back hand).
When you sense that you're nearing the ground, let go of the snowboard. If you don't want very bad things will happen to your poor hand, which of course did nothing whatsoever to deserve such a cruel fate. Anyway, as you let go, brace yourself for the landing. Bend your knees.
Step 6: Landing
Step 7: More Grabs...
Work on improving them, maybe tweak them a little bit, throw in a shifty or two, a rotation, anything you feel like. Have fun, and don't die!