The molten metal is extracted through taps which are, usually, in the bottom of the cupola. Cupolas have provisions called tuyeres in the side to feed fresh air to the coke to obtain higher temperatures.
The cupola furnace is filled with coke. At the bottom, a layer of wood is placed and ignited. Air is blown through the side channels. The metal to be melted is placed on top of the cupola. The coke burns in the air to form carbon monoxide, which on further oxidation becomes carbon dioxide.
As the molten metal comes down the cupola, it reacts with the oxides of carbon. This produces metal with a high carbon content.