Air handlers and furnaces aren't typically found in the same home in Austin. If you rely on a furnace, you probably don't need to spend time thinking about an air handler.
Air handlers are typically linked with heat pumps and control airflow across your house. Some models also offer secondary heating and cooling components to support the heat pump.
A furnace heats in a different way by blowing warm air into your vents, which move it throughout your house. Because furnaces rely on combustion chambers to create warmth, they don't use some of the components you'll see in a regular air handler.