It's important to not confuse a hookah with a bong. A bong has a solid mouth piece at the top of the device. A hookah has a flexible tube leading up to the mouth piece that you suck the smoke out of. Usually used for tobacco smoking, a hookah is nice to smoke weed out of, as well. Sometimes cannabis users mix it with flavored tobacco to enhance the initial buzz and give your high a particular taste. Flavored pipe tobacco can be purchased in a variety of delicious kinds, so find one that you like the most if you're trying a hookah.
The difference between smoking a hookah and a blunt, for example, is that you can't control how much smoke you inhale as well. With a blunt, or a pipe, or a joint, you inhale the THC in your mouth first, and then breathe it in with air. If you're using a hookah, you inhale the bud directly into your lungs. This leaves you little control over how well it'll hit, and how much smoke to actually breathe in. The science behind how it works is complicated, and involves a bit of chemistry. Using convection and conduction, you need to apply just the right amount of air pressure when sucking the smoke in. No wonder it's harder to hit a hookah right than a bong or a can! Basically what you have to do is create lower air pressure at the base of the hookah than at the top. Much like a bong, this causes the smoke to filter through water, or whatever other liquid you decide to use to cool your smoke. The benefit of a hookah is that you can control the proper amount of heat transfer by moistening your bud prior to the actual process of smoking weed. That's how it's intended for tobacco, so that's how it should be done with bud, as well.
A piece of tin foil with pinholes (can be done with a thumbtack) can act like a screen for your hookah. This can aid in airflow regulation and air pressure disbursement in the device. Putting ice in the liquid chamber is proven to be a good idea to cool the smoke down extra cold, for easier inhalation. You need to fill up the tobacco chamber about an inch, and put a lighter to it as you're about to hit it. Don't pack the bowl too tightly, or the smoke will have little room to go through, and this will mess up the whole process. To keep the hose clean, blow hard through it to get anything that may be stuck inside out. The tinfoil that was mentioned earlier goes over top of the bowl with weed, to keep heat spread out evenly. About thirty to forty holes should suffice. The proper way to smoke a hookah is to put a piece of coal over the tinfoil, but if you don't have that, just use a lighter and move it over the tinfoil evenly.
Smoke up, and enjoy your hookah responsibly!