Brian,
The way that I relate exposure to people is to explain that a given film will require a given "quantity" of light to expose it. There are in photography two different "controls" to affect this quantity of light. The first is the size of the aperature or "opening" through which the light passes. The second is the length of time that the opening is open "Shutter speed".
The important thing to remember is that the measurement of apertures and of shutter speed is a ratio of doubles and halves. Thus if one reduces the opening by one half the offsetting factor would be to allow the opening to be open twice as long. This effectively gives the same quantity of light. Conversely if one opens the opening by twice as large, then the offsetting factor would be to allow the opening to be open only one half as long.
Once the quantity of light is determined by a light meter, either in camera or hand held, the user determination is one of "depth of field"or of shutter speed (ability to stop photographed subject movement). The more the opening is restricted the greater the depth of field (near to far plane of focus). The more the opening is increased the faster the required shutter speed to compensate. (Higher shutter speeds stop movement). I hope that this helps and gives you some idea of how to present this to your friends in your own words. Good luck.