You will have to defend your tower by purchasing different weapons and placing them strategically so enemies may not pass by. Towers can be upgraded to increase their power. There are several weapons you can use to prevent them from attacking. Some of those are- Vulcan turret, plasma turret, SAM turret, DCA, freeze turret, sonic turret. The game has different levels and each of these levels is harder than the previous one. There will be waves of enemies coming toward you. At first, you will need to place your weapons in the map to make obstacles in their way. As the enemies move forward, the weapons will automatically launch attacks to kill them. Stronger enemies will come in further levels and to kill them, you will need to apply more weapons and set those on their way to block their movement. Remember; always try to block the entrance of your basement. So, use the heavier weapons there.