If you don't know how they work, read on.

The coffeemaker is a two part pressure device with the coffee held in an internal funnel. The bottom part is filled with water, the coffee funnel inserted and filled with coffee and the two parts are then screwed together. Put the assembled coffeemaker on a cooker and as the water boils the pressure generated forces the water through the coffee, up a central pipe and overflows into the upper container. When the bottom half starts to boil dry then there is a satisfactory noise (a bit like the sound you'd make if you were being strangled!) at which point you remove the coffeemaker from the heat and serve. Easy!