The basic idea of Exposure in regards to photography is how bright or dark an image is.
If an image appears too dark, it is known as underexposed, and if it is too bright this is considered overexposed.
Normally, an appropriate balance is needed between the two in order to produce a sharp and appealing RAW image, but then again, it is up to the photographer as to how they depict their subjects and how they assemble their lighting and exposure.
Examples of well-balanced and exposed photographs.
When it comes to deciding how to expose the subjects in your photograph, you can look to the ‘Exposure Triangle’; manually, this is the arrangement of Aperture, Shutter-speed and ISO.
Aperture, in simple terms, captures the light in your photograph. The larger the aperture, the brighter the image. However, it is worth noting, that to do this, it means you need to manually use a smaller F stop on your camera (the smaller the F stop, the larger the aperture). The aperture is usually increased in darker photographs and increased in brighter photographs.
However, Aperture also affects your camera’s Depth of Field, which is how much is in and out of focus. The wider the Aperture, the smaller the Depth of Field.
An example of a potentially underexposed photograph.
Shutter-speed is known at the 2nd part of the Exposure Triangle, which looks at freeze motion. The change in Shutter-speed (to make it faster) allows less light in to your camera, which not only helps you balance your lighting but also ensures no blurring if you are taking a photograph of a subject in action.
Tripods are very useful to avoid shutter-shake when you are using a slower Shutter-speed. Examples such as 1/80 or 1/100 also allow you to avoid shaky imagery.
An example of a potentially overexposed photograph.
Finally, ISO is the level of sensitivity to the light which hits the sensor in your camera. If you were to increase your ISO, this would equal in a brighter image, however there is a tendency to lose quality – by enhancing your image this equals in more noise or grain to be within your photograph.
For no noise, ISO 100 is most satisfactory. But remember, that to increase ISO when dealing with very dark subjects is not necessarily a bad thing.
It is quite difficult to balance all three concepts, but a helpful start would be to always drop ISO to 100 when it comes to daylight photography.