If the game freezes, just click inside it (games can get unresponsive if you click elsewhere on the page).
Get on a turtle shaped tank and get ready to shoot the enemy. You'll get money every time you defeat them, and you will be able to buy better tools.
W,A,S,D - Move.
Mouse - Aim / Shoot.
Q,E - Special Attack.
Spacebar - Weapon Cycle.