Yep, what Mr Wolf said. Basically, its a series of alternating nose and tail presses. To get the forward movement you, for example, spring off your left leg and throw your right shoulder (and torso)UP AND FORWARD. It will also help if you try to pull your right knee up and try to stride forward as you throw your right shoulder (this helps to get more flex in the board for more spring). The net result of all this is that your board will leave the ground, rotate in mid-air and when you land, your right foot should in front of your left foot.
The next step is to keep this movement continuous. So following from that above, when you land, land with your right foot on the ground and into a press and almost instananeously throw your left shoulder UP AND FORWARD etc. And repeat. Needless to say if you dont land in a press and land with both feet on the ground or with a reasonably flat board, you kill the momentum, risk catching an edge and gotta start all over again.
Most probably, you are not going to get very much going at first, so even 1 or 2 steps is probably all ur going to get. But the key is quality and practise (like Mr Wolf mentioned). One more thing is that most people thing its just a "forward only movement with bending the board". To get the most out of it u have to be LEANING INTO A PRESS before u extend the pressed leg and throw ur torso UP AND FORWARD otherwise the power from the nose and tail rebounding do not assist you and u end up just trying to tug the board everywhere. It can be done, but its uglier and relatively ineffective. So remember to bend sideways and load the tip and tail by shifting ur weight before popping off.
Its easier to learn this on a lighter softer board, but once u get good at flexing and popping a board, u prefer something stiffer cos its actually easier in a board with more rebound to it.
Lastly, u need practise time. Try strapping in a good distance away from where ur going to start riding from so u can practise this movement before each run. Try also to end each run about 20 metres short of where you unstrap so u can practise this at the end of each run. Good Luck!