Exposure: the amount of light allowed to fall on each area unit of a photographic medium (photographic film or image sensor) during the process of taking a photograph.
Three important elements in a photo:
-Aperture: Size of the opening of the lens while the photo is taken.
Smaller the number, larger the aperture.
Larger the number, smaller the aperture.
-Shutter Speed: amount of times the shutter is open.
Slower the shutter speed, the more blurry the photo becomes.
Faster makes it clearer and sharper.
-ISO (film speed): measure of a digital camera sensor's sensitivity to light.