Basically, lay on your back, lift your legs up, and pretend you are riding the bike. The video shows it best, but know that you don't have to move your back/stomach, it's just that it helps even more if you do.
I'm an advice-giver, listener, and psychiatrist by day
and a wild, party-starting, life-of-the-party male entertainer by night
I exist to explain dreams
And then I aim to fulfill them
I am here to keep it classy
And then I am here to party
I will be selling at San Japan