Quickly described, a weed bong is the same thing as a waterpipe but without hoses. The difference is minimal, with a regular water pipe one slowly draws the smoke trough the hose and the water. But,
with a weed bong the smoke will pass the water in one bang because of pressure difference, thus this is why a bong is called a bong !
Some say that asian are the ones to thank for the shape of these water pipe ( weed bongs ).Some suspected that bongs are older than the waterpipes, predecessor of its Indian members. People ( especially in amsterdam ) generaly use bongs to smoke what is called today softdrugs which is know as : weed, marihuana, weed, pot, cannabis and other obscur local terms that I wont mention here ;)
On top of each weed bong you'll find a bowl in which you place your smoking herbs. The smoke passes through the liquid ( usualy water ) before getting to the mouth. Some of carcinogens like tar are filtered by the water / liquid. The water also cools the smoke. Using weed bongs allow smoke to be inhaled alot more deeply and rapidly. Results is increased efficiency , thus less weed is needed.
When smoking a weed bong don't use tobacco. use pure weed. By not using tobacco you will only get pure weed elements in your lungs creating a clearer feeling. Tobacco has opposite effect :mixing of tobacco with weed makes you dull and tired faster. You also need to smoke more to feel good.