If the game freezes, just click inside it (games can get unresponsive if you click elsewhere on the page).
Defend your castle from the enemies. They are attacking your castle using gun and cannon. You want to kill all of them to defend the castle. Using your guns destroy all the enemies and get more points. Using that points buy powerful guns and also increase the health of the castle.
Mouse key to shoot the enemies.
1 to 5 keys to change the gun.