* Alternator: Charges the battery.
* Power Steering Pump: Assists in steering.
* Water Pump: Circulates coolant.
* Air Conditioning Compressor (if equipped): Compresses refrigerant for air conditioning.
* Idler Pulley(s): Provide support and routing for the belt.
* Possibly others: Depending on the year and specific options, it might also drive the power steering pump or other accessories.
In short, the serpentine belt's function is to transfer power from the crankshaft pulley to all those accessories. If the belt breaks, none of these accessories will function.