your mission is to defeat all your enemies. When your energy charges, you are in the defense mode which means you have no weapon to select so that you have to defend the space eye from enemies? attack. Some weapon needs 1 bar energy to be accessible while some others need 2 or 3 bar energy. When the needed energy bar has been fully charged, you can select weapon and enter the attack mode which means you can kill enemies at this time. You will be protected by an energy shield whose energy decreases all the time. When you use up your energy, you will reenter the defense mode. Good luck!