If the game freezes, just click inside it (games can get unresponsive if you click elsewhere on the page).
Its a shooting game.There are Zombies are appeared on the screen . you to shoot the Zombies within time limit .if you achieve that then you can proceed next level. otherwise you try again until the level finish
1. click the start button
2. using mouse pointer to move the shooter in that area
3. click the left mouse button to shoot the zombies