If the game freezes, just click inside it (games can get unresponsive if you click elsewhere on the page).
Vikings got it right: the Hammer is the Weapon of the Gods. Little creeps are trying to get into your tree. Beat the living daylights out of them! Upgrade to massive hammers like Frostbite and Volcanic for even bigger smashies!
Mouse key - To beat your enemies.
A/D Letter keys - To move.
1-8 numbers keys - To toggle weapons.