The bowl is the portion of the bong that holds and heats the cannabis buds. The downstem, a cylindrical glass component with perforations that connects the bowl to the bong, filters the smoke through water. The smoke passes up the neck and into the mouthpiece, where it is inhaled.
Bongs are preferable over pipes because they deliver a smoother hit. Some claim that the water filters out a small number of terpenes and cannabinoids, although it is trivial.