The idea is for the rider to jump with his board and then ride the rail all the way to the other side. Land on his board and feet and then continue. Shaun and most other riders practise all day on a few different manouvers in order to perfect them. Here he finally succeeds. This entire manouver happens in a few seconds and at a fast speed. One has to anticipate when to take the shot.
I admire their determination, quest for perfection and desire to succeed.