Defense Commander is a non-stop action game of fast-paced defense of you and your buildings. You're in control of the main weapon and you'll use the mouse to aim and shoot at the enemies coming from above. If you want to fire a special bomb you can press the space bar. You'll have units on the ground that can help attack and repair. If a building needs to be repaired you can tell by the green bar at the bottom. If it's getting short, put your mouse over it and you'll see a wrench. If you want to upgrade your defenses, press the upgrade button at the top of the screen. Every level has a different objective and has hours of fun for you in Defense Commander.