Shutter Speed: The shutter speed controls the time aspect of exposure by controlling how long, or short, the shutter stays open. A longer shutter speed will allow more light to enter the camera and hit the image sensor, such as 1/30th of a second. The shorter the shutter speed the less light that will hit the sensor, such as 1/500th of a second.
Aperture: Aperture, or the diameter of the opening in the lens, controls the amount of light that can reach the sensor. Smaller f-stop numbers, such as f3.5, allows for more light to hit the image sensor. A larger f-stop number, such as f22, will allow less light to hit the sensor. Note: Aperture also controls the depth of field in a photograph. The aperture range is based on the lens itself, not the camera.
ISO: ISO determines how sensitivity the camera’s sensor is to light or in other words how fast it collects light. A lower ISO, such as 100, means the camera is less sensitive to light. A higher ISO, such as 800, makes the camera more sensitivity to light.
Proper Exposure (Putting it all together): All three components work together, yet independently, to create proper exposure. The shutter speed and aperture have an inverse relationship. If you turn the aperture down one f-stop, say from 4.0 to 3.5, you double the amount of light in the exposure, so in order for you to have proper exposure again, you have to increase the shutter speed by one click thus halving the light in the exposure. You might be asking yourself how do I determine what is a good exposure? Well, both in the viewfinder, and on the LCD display, there is a meter that shows you the exposure level for what the camera is pointed at. The middle, or zero, would indicate a proper exposure. The negative side would indicate an underexposed photo and the right side would indicate an overexposed photo. There are a number of ways to get the same exposure level for any given photograph. For example, a shutter speed of 1/50, f-stop 5.0, ISO 200 would be equal to 1/60, f4.5, 200 or 1/80, f4.0, 200. If you were to bump the ISO up to 400 (one change in ISO equals to 3 clicks of shutter speed or f-stops) so then exposure would equal 1/50, f 7.1, 400 or 1/100, f5.0, 400 for the same scene.