Shoot every zombie that speaks bad English. If the zombie hasn't said anything wrong, shoot the speech bubble. Shoot apples, bananas and melons to gain more points. The health pack replenishes one 'health' (one life). Watch out not to get blind, because you'll lose sight for 5 seconds.
Press the left mouse button to shoot. Every shot uses a bullet. When you run out of bullets, press the left mouse button to automatically reload your ammo.