Imagine you're flying at night and this is the view out the cockpit window. Those blinking lights (white, red, and green) tell you the path to follow to get you to your destination (waypoints) or where airports are located.

In the days before radio navigation, beacons were used to indicate where airports were located during night flying. Airports in a given area used different colored lights and flashed at different rates so pilots could distinguish them.

A beacon would, for example, flash white, then red six seconds later, then back to white six seconds later.