The main object of the game is to defend and expand your colony. The way to do this is to complete objectives and missions that are linked by the overall storyline into episodes. You can always see your current objectives on the left side of the screen.
If you don’t know how to perform the actions necessary to complete an objective, click on the “Start” button to see a hint.
Before you start a battle you should check your munitions and the combat readiness of your troops in the “Troops” section.