Your objective in The Lost Planet Tower Defense is to line the road with numerous towers and machine gun posts to prevent the adversary from passing.
Use the battery to locate new land, conquer all the levels in an area to unlock new items, earn ranks to collect some items, save some aliens, and be the first to reach the level of completion. Use the mouse to interact with the environment and make decisions in order to clear each level and be able to combat any incoming alien onslaught in order to conquer the entire planet.
Have fun and good luck!