ISO – The level of sensitivity of the camera to available light. If a subject is well lit, then a lower ISO value is appropriate such as ISO:100, as the camera will be less sensitive to light. However, increasing the ISO value brighten the subject, at a cost. The higher the ISO, the more noise and grain in the image.
Shutter Speed – The length of time in which the camera sensor is exposed to light. These values are often measured in fractions of a second. The slower the shutter speed, the more light entering the camera, often used for low light or night photography. A fast shutter speed is used to freeze motion. For example, a faster shutter speed would be used for action sports photography.
Aperture – A hole within the lens that allows the light to travel through into the camera body. The larger the hole, the more light that travels through. Aperture also controls the depth of field, which is the part of the frame that appears sharp. Aperture is defined by “f” stops, (also known as “focal ratio”, since the f-number is the ratio of the diameter of the lens aperture to the length of the lens). For example, F/1.4, f/2.0