Your mission in this tactical defense game is to defeat all kinds of aliens by strategically placing firing towers onto the map. Use YOUR MOUSE and click on a tower to select it (info about that tower will appear beneath it), once you selected a tower, move the cursor onto the map. The green box shows where the tower will be placed. If it goes red, you cannot place it there. When you have placed enough towers on the map, press Start button to face the first wave of aliens. You are getting money for killed aliens. Use this money for buying more towers or for upgrading the existing ones. Good luck!