Defend your main tower from enemies by clicking to select and place (a) cannon(s) and then clicking the approaching enemies to target them. In the building phase, select barriers and place them around the main tower to create a wall. Complete the wall before time runs out! The more land you enclose, the more money you earn and cannons you have at your disposal. Before facing each new wave, you'll be taken to an upgrade screen where you can spend your money. Tip: Use your building time to repair walls, and then build another layer of walls around them!