depending on where you are from the different parts of the bong go by different names, eg. aussies call the ice cream cone shaped thing you put the pot in a cone piece or cone for short where as americans call it a bowl

anyways, here is a simple diagram with an explanation on how to use the bong and im sorry about the quality of the pic, im not gifted in mspaint
Click to view attachmentthe rectangle thing is a bottle which i forgot to lable but shit happens, the end of the stem needs to go into the water, the cone piece sits at the end of the stem and you then place your thumb or finger over a small hole above the water line and then suck gently. since the only way for the pressure to equalise is to get more air into the bong, air gets sucked through the cone piece, down the stem and then into the water which then goes upto the mouth piece of the bottle. once you have pulled the cone, you can take your finger or thumb off that hole above the water line and continue to suck gently and it will clear the chamber of smoke

alternatively you dont need to have that hole above the water line in which case you can break the seal around the mouth piece your lips are making or you can pull out the cone piece and heaps of air will get sucked into the bong eventually freeing up the chamber of smoke...
bong smoking 101 has now come to an end, i suggest getting some practice for homework