The electric aerial receives radio waves so that you can listen to the radio in your car.
The electric aerial is fixed to the outside of your car, usually contained within a vehicle section or the window frame on the driver's side. The electric aerial is connected to your car stereo by an aerial cable which houses the conductor needed to receive radio reception, and the electric aerial is basically an extension of the center conductor inside the aerial cable.
The electric aerial is operated by a motor and can be adjusted automatically from inside your car. It is usually operated by a small button which starts the motor. In some cars the automatic aerial may also function when the car radio is switched on or off. You can extend the electric aerial fully to improve radio reception or retract it back into the body of the car when you're not listening to the radio, which is a useful function in avoiding weather and accidental damage to the electric aerial.
The electric aerial, like most electrical parts, does have a lifespan and will eventually need replacing. But careful and regular cleaning to avoid damage from dirt will ensure the electric aerial lasts longer.