The goal of the game is to destroy the enemy mothership by changing the force balance.
You must not let the enemy units to get to your ship, instead you have to get your units to the enemy ship. You win when the balance bar becomes filled.

Change the current hatch/road by pressing UP/DOWN on the keyboard.
Select current unit by pressing LEFT/RIGHT. Press SPACE in order to send the unit.
Alternatively, you may use and click on the unit buttons directly.
Every minute the Storm Attack is prepared and 5 units of a selected type go from all the hatches.
If neither side wins during 3 minutes the Final Attack starts and units of all available types go from all the hatches. The party which is ahead after the Final Attack wins.