They'll usually teach you a front flip before a back flip.
To throw a front flip come up to the jump, raise the roof, and pop forward dropping your chest/head
Landing is somewhat blind, the jump should have some kick, a powder landing is ideal
Things to remember when trying your first backflip
centred over your skis
move with your core
don't over emphasis by throwing your head
it's more in your ab's and tucking or stretching out your legs to speed up or slow down your rotation
I'd recommend try your first one on a 1/4 you only need about 2 feet of air, if things go wrong drop your shoulder and look down you'll atleast throw a flair. even if you don't land it you'll get a sense of whether flipping is right for you or not
Don't forget your brain bucket for either
If you can't competently do either off a diving board or on a trampoline disregard above statements.
and water ramps are the safest way to go.