Make sure you have a solid 3, 5, 7, etc. If you're doing a 5 or more, throw it like a normal spin. Have your feet about shoulder width apart and set your spin as you pop. The difference is, where normally you would look at the horizon, you now want to look back at the ground about 100 feet behind you and drop your lead shoulder a bit. (Left shoulder if you're spinning left.) From there, you just tuck it up, keep looking over your shoulder, and watch for your landing to come around. Don't open up too early though. Stay tucked and the trick will complete itself. Corked 7's are generally the easiest.
A corked 3 is a whole different trick. You'll want to carve your takeoff, using your carve to set the spin instead of throwing with your arms. From there you drop your shoulder, tuck up, and wait for the trick to come around. These, at least for me, are much harder than 5's, 7's, etc.
Anyway, good luck. If you can, try them on a trampoline or diving board first.