And here's another picture:
You stand with your foot on one end of the chain; the end with the screw goes into the camera, as many of you already thought. Then you tighten the chain - et voila, you can take picture with a longer shutter speed. It's not as firm as a tripod, but therefore small and easy to carry with you.
The chain camera stand from the second picture you can fix with your both feet, so you even got a more firm stand.