What Does Exposure means?
The exposure is the amount of light received by sensor that is dependent on how wide we open the aperture or how long the shutter will remain open (depending on the shutter speed).
How Important it is in Digital camera Photography?
The exposure value depends upon the Aperture, Shutter Speed & ISO levels. the combination must be set in a way that the image looks perfect.
For beginners we prefer to use Automatic shooting mode or the set shooting modes by Digital cameras as tn automatic mode, the camera itself determines the most useful combination of aperture, shutter speed, and ISO.