is a type of bulk vending machine that dispenses gumballs, usually for a small fee.

3d animation:

Views from top, left and front sides:

Generally, a gumball machine consists of a clear sphere (originally glass, now most often plastic) which is filled with gumballs, sitting on top of a metal base. 

It has a metal top on top of it with a keyhole in top of it so that the top can be removed and gumballs can be put in. The coin is inserted into the base and a handle is turned around clockwise 360 degrees, depositing the coin in the base of the machine and allowing a gumball or trinket to be dispensed into a chute at the bottom of the machine that is closed off by a little metal hanging flap.