Hey there kiddo, do you know what a heater is? It's a machine that can warm up your house or room when it's cold outside. Some heaters use gas to create heat and this is called a gas heater.
Forced-air gas means that the heat from the gas heater is blown into your home through something called ducts. Think of a duct like a straw that runs through your house and it blows warm air out of the end of the straw. These ducts go through the walls, ceilings, and floors and they deliver the warm air to every room in your house.
The gas heater produces flame, and that flame heats up something called a heat exchanger. The heat exchanger is like a metal box that gets hot when the flame is touching it. The heat exchanger is where the heat is made, and then a fan pushes air over the hot heat exchanger. This warms the air as it flows past and then this hot air is pushed through the ducts in your house to keep you warm and cozy.
Forced-air gas is a common way to heat homes in many places, especially in colder parts of the world where it can get really chilly. It's a great way to stay warm and cozy inside while the weather outside is cold and wintry.