You must win each race in order to unlock the next track, and the difficulty increases the farther along you go. Each race is only two laps, but on the harder tracks it can be tough to keep your lead for that long. The main reason you'll find that it's hard to stay ahead is the unique control scheme: steer with the arrow keys while aiming and firing your turret using the mouse. Even after several races you'll find yourself occasionally overwhelmed by the task of firing in the opposite direction that you're steering and run yourself right into a wall, cursing a blue streak as the computer opponents pass you by. Shooting is more defensive in this game than offensive. The tanks take a lot of damage before blowing up (which, unfortunately, they don't really do, they just sort of fizzle out), but when a tank is hit it stops dead in its tracks. That may be your main tactic: get out in front as early as possible, aim your turret behind you, and start shooting at your opponents to keep them at bay. It's hard to climb out from last place because you're every one's target.