The idea is to crash into as many things as possible to increase the amount of damage (in dollars) caused...
You can steer with the sticks and lean the sixaxis into things to move your wreck down the road.
Your boost bar becomes an explosion, so tapping the boost button causes your car to explode forward into the traffic.
The more cars you hit, your boost bar replenishes and you can therefore keep the combo going... if you don't hit anything and stay still your boost bar will run out and showtime finishes...
(buses act as multipliers to your score, so hit a bus and yu get 2x, next bus you hit it becomes 3x etc etc etc)
did that make any sense?