Try the exercise here. Set your camera to manual and find a shady spot.
The primary function of these lens openings is to control the volume of light that reaches the film or digital media during an exposure. The smaller the f-stop number, the larger the lens opening; the larger the f-stop, the smaller the lens opening.
If my camera is set for ISO 100, I have, in effect, 100 worker bees; and if your camera is set for ISO 200, you have 200 worker bees.