You've to help him shoot and hit other obstacles before the time runs out to proceed to the next level.
Spaceman   Fish Money   The Plumber   Tribal Jump   Global Rescue   Mud Ball   Zombie Horde 2   Jingle Ballistic  
There are lots of different levels and you need to hit various targets before the time runs out.Use LEFT and RIGHT ARROW KEYS to look around and locate your targets. Then click and drag THE MOUSE to set angle and power of your shot.
See Instructions

Invisible Cursor However, it is not that easy as your cursor is invisible. To start click the go button and then try to move your mouse to stop button. If you reach it, it gets darker. Click it to continue to the next level. It becomes pretty hard around level 5.