If the game freezes, just click inside it (games can get unresponsive if you click elsewhere on the page).
Your mission if you wish to accept it, is to protect your country at all cost. The game is an Assassination Simulator to help you become the best! You should try to shoot all targets as soon as they appear and don't forget to refill using the Space bar. Each time you miss you will lose a life. As you progress the targets will get faster.