The idea behind light painting is that if you open the shutter, you can draw lines by moving the flashlight around in front of the lens. So hold the shutter open, get in front, and try drawing something in the air. If you have a camera flash, you can have someone stand in place, and flash them. Then have them hold still and draw around them. Experiment!
Here’s a behind-the-scenes look at how Light Warfare was made.