How does a bong work?

It's actually pretty simple, you light the slide piece holding whatever it is you are smoking, it goes down a tube on the bong and goes underwater, the sucking motion is pulling air through the slide and down the tube. The air at the bottom of the water is trapped, and the only place it has to go is up through the bong and into your mouth, this is why a bong bubbles, I hope I explained this well enough.