Destroy the enemy base while defending yours. You can build turrets to defend your base and units to attack the enemy's. The twist of the game is that you can evolve as well as unlock new units and defense means.
In the year 3012, the people of Earth desperately searches for a new planet for survival. When they found a star near Epsilon Eridani that had water and similar atmospheric properties to earth, they learned that there was someone living there...