Hold the mouse down to shoot. Hold the A key and mouse down to drag the turret to where you want it to go.(You can only place a turret on the dark gray). Press the space bar to release the aliens! (Hold the space bar down to release a horde) Note:the aliens don't die right away, they have a few lives.
Thanks to griffpatch for the turret. There is one glitch where you can place a turret even if you don't have enough money, but the turret won't work until you get enough money. If you accidentally place a turret on the light grey, it won't work, and it will go away once you drag out another turret.
