Hopefully this will help:
1) As the cars/trucks etc go by, you "release" some air

- You do this by pressing the space bar. You need to be careful not to press it for too long or the man beside you will hear you.
2) The "Cont" bar is the amount of air building up. If that goes up into the red, he will shoot off.
3) The "Ctrl" button is used to control the amount of air. You can use that to bring the air back down in the "Cont" bar, so it doesn't go into the red. You have to use this sparingly as when it's gone, you could be in trouble.
4) The more air you can "release" as the cars go by, the better. If you reach a certain level of air releasing, you win some more "Ctrl"
I think that's about it !! Good luck.