The flames from the burner component heat a metal heat exchanger. The heat circulates through the looped tubes of the heat exchanger, transferring the heat to air.
If you smell gas (sometimes described as a rotten-egg smell), do not operate any electrical components. Evacuate the home and then call your utility company or fire department. Do not reenter the home until a professional has deemed it safe to do so.
The main parts of your furnace are the control system (thermostat and electrical controls), gas valve, burners, heat exchanger, blower, and duct and ventilation system. When your furnace creates heat, combustion gases are vented out of your home via a flue pipe.
Test your smoke and carbon monoxide detectors every 30 days to make sure they are working properly.