You can control the amount of light that reaches the film in two ways: by adjusting the amount of time the shutter stays open (referred to as the shutter speed) and by changing the aperture.
The aperture is a hole in an adjustable diaphragm set between the lens and the shutter. Light coming through the lens is funneled through this hole to the shutter and then onto the film. So if you want more light to strike the film, you make the aperture bigger; if you want less light, you make the aperture smaller.
Shutter speeds are measured in more obvious terms: fractions of a second. A shutter speed of 1/8, for example, means that the shutter opens for one-eighth of a second. Try to capture a moving object at that speed and you wind up with a big blur. You need a shutter speed of about 1/500 to capture action clearly
The three settings work together. You can play with setting on this tool