Photography is the art of using a camera to record an image through the use of a lens. In this process, there has to be light. Otherwise, you will not be able to capture the image. This shows that the light used in photography is paramount. Every photographer must know how to work with the light to capture the best image. This is where exposure comes in.
Exposure can be loosely defined as how the image is captured and recorded by the camera sensor. It also determines how much light is captured which in turn contributes to the quality of the image you capture. Exposure is determined by three elements: ISO, Shutter speed and aperture. These three are said to form the exposure triangle.
ISO refers to how sensitive the camera sensor is to light. If you want to increase the sensitivity to light, then you deal with a higher ISO value. On the other hand, a lower ISO value is best used to reduce the sensitivity of the sensor. If you are operating in lower light conditions, you want to have a higher ISO value. The contrary also holds, that is, if you are operating in high light conditions, you would be better placed using a lower ISO value.
Apart from the light conditions, you would also need to understand how light contributes to the saturation level and the noise captured by a photo. ISO 100, for example, will account for more saturation and therefore lead to better details in the photograph. On the other hand, a higher ISO such as 400 will have more noise and less saturation.
Shutter speed controls how long the light reaches the sensor of your camera. The shutter is the click that you her whenever you take a photograph. Therefore, the shutter speed is how fast the shutter closes. The faster it closes, the less the sensor is exposed to light. This is measured in fractions of seconds. You can then choose to understand it in one of two ways: the larger the second figure/ denominator, the faster the shutter speed or the smaller the fraction, the faster the shutter speed.
Aperture controls the amount of light that enters the camera. It is a hole or opening in your camera lens that regulates the amount of light getting into the lens. The size of the aperture is determined by f-stop values. The rule of thumb is that the higher the f-stop value, the smaller your aperture size. This means that less light will get into your lens. If you have smaller f-stop values, the opposite is true. Smaller aperture size enhances your depth of field, capturing objects or people in clearer details. However, if you want to have a shallow depth of field then you need to use a larger aperture size which corresponds to smaller f-stop values.
You must know how to work each of the three elements if you are going to grasp the exposure triangle. You can start off with one and then work your way to learn the three.