Click Start Patrols in the middle of the screen. Then click the stage on the left side of the screen. While there are two other stages you can play, you first have to unlock them. Your first mission is to capture a drug kingpin who managed to avoid being caught by a sting operation. Once you finish reading the onscreen briefing, click Start in the lower right corner.
This game requires you to use a combination of keys and your mouse. You can use the left and right arrows to steer your patrol car so you avoid hitting other vehicles. You will also use your mouse to aim and fire at the fleeing kingpin, as well as the spacebar to reload your weapon. As you progress and collect additional weapons, you will be able to use the 1, 2 and 3 keys to switch between them.
ARROW KEYS and W,A,S,D: control police car
LEFT MOUSE CLICK: shoot
1,2,3: change weapons