Refer to figure.
Just like driving an automobile, Pilots also must learn and obey Traffic Light Signals. You might wonder why a Pilot would need to use Light Signals when they have a Radio for Communication. In fact, as a pilot you will seldom use light signals. However, radios sometimes stop working. In the event of a communications failure, you will need to fall back on Aviation Light Signals for communication.

Air Traffic Control (ATC) will use a powerful Light Gun to Signal the Pilot in the event of Radio Communications failure or other emergency when the pilot does not have a working Radio in the aircraft. When a pilot is flying with No Radio, they must watch for the Aviation Light Gun Signals from the Control Tower.

For flashing red light signal towards an aircraft on the ground it means you have to immediately taxi clear of the runway in use.

NOTE:
The easiest why to remember the light signal procedures is to refer to the attached figure and memorize the figure by drawing it yourself.