A Gas fired furnace creates heat by burning natural gas or propane and distributing the heat to the house. The Electric Air Conditioner takes heat from the house air (cooling the house) and gets rid of it to the outside air.
A Heat pump System (all Electric) is an Air conditioner that can run backwards. Instead of moving the heat from inside to outside (like in the summer), it reverses operation and moves heat from outside air to the inside air (heating the house)