The Bong
A bong is a popular method of smoking marijuana. Marijuana is placed in the bowl and burned, while smoke is inhaled through the top of the shaft. Water is placed in the bong, and should be filled approximately to the white line in the diagram above. Smoke travels through the drop-pipe (connected to the bowl), through the water, and finally out of the top of the shaft and into your lungs. But be careful not to put too much water in, because: a. it could travel up the drop-pipe and wet your weed, and b. you could suck in a mouthful of bongwater, which is not nice.
The water purifies and cools the smoke. You'll be taking bigger, better tokes out of a bong. Some people choose to drink the bongwater afterwards... this is a brave thing to do. If you wanna impress someone, drink the bongwater... although I still don't recommend it.
Making Your Own Bong
A quality bong is not hard to find, but it can cost alot of money. If you have the money, a glass bong from a head shop is a great investment. But if you don't have the money, or are just a cheap bastard, you can make your own.
First of all, you'll need your main part, the shaft. It needs to be long, hollow, waterproof, and you need to be able to put a couple holes in it. For example, a pop bottle or a pringles container would both work, because they can both hold water, and it's pretty easy to poke a hole in either one.
Secondly, you'll need a thin, long tube for your drop-pipe. It needs to be waterproof. It should not be any longer than half the length of your shaft. Now get something to use as a bowl(remember, it can't burn), maybe just off the nearest pipe, and attach that to one end of your drop-pipe.
Now poke a hole, just big enough for your drop-pipe to fit in. It should be just high enough so that the bottom of your drop-pipe almost touches the bottom of the shaft. Put your drop pipe in the hole and seal it so that it's airtight, using something like sticky-tac, or chewed gum. Your drop-pipe should be sitting on a diagonal.
Now here is where you can get original. You need somewhere to inhale out of. If you're using a pop bottle as the shaft, obviously, you can just inhale out of the top. Basically, all you need to do is have a hole of sorts either on the top of the shaft, or somewhere near the top. Keep in mind you will be inhaling out of it.
Now fill the shaft with water so that the water doesn't travel up the drop-pipe into your bowl. I assure you this would suck if it happened. If you need to, use the diagram at the top of this page as a guide.
Your makeshift bong is now ready for use. Light the weed in your bowl and inhale through the hole on top (or near the top) of the shaft. If you suck really hard, the water should bubble. If not, you may have an air leak somewhere on your bong. Check mainly around where your drop-pipe enters the side of the shaft.