Okay little one, have you ever played with straws and blowing bubbles in your drink? Well, a gravity bong is kind of like that, but for grown-ups.
It starts with a big container filled with water, like a bucket or even a bathtub. Then, you need a smaller container, like a plastic bottle or a glass bowl, with a hole at the bottom.
You take the smaller container and fill it with some smoking material, like tobacco or marijuana. Then, you put it in the big container of water, with the hole facing up.
Next, you light the smoking material and slowly pull the small container up, which creates a vacuum that pulls smoke into the bottle. Once it's filled with smoke, you take the small container out of the water and inhale the smoke.
This can be a pretty intense way to smoke, so it's important to do it safely and with caution. And remember, it's not for little kids like you, only for grown-ups who are legally allowed to smoke.