Always make sure the end of the bowl tube is under the water, if it isnt you wont hear a bubble and your hits wont be filtered.

theres a couple ways to put water in it, you can pour it in the bowl, or you can put a water bottle to the carb and pour water in that way, always dump the water out the carb, keeps the rest of the bubbler cleaner.

here are some more pics of different style bubblers, the first one is a double bubbler, where the smoke gets filtered twice once in each chamber before you inhale it.