-When shutter speed is too slow or the aperture is low and the lens is letting too much light in the photograph may be overexposed. This creates a very bright image with lots of white areas and therefore many details are lost in the process, as in the first photo. Sometimes using an overexposed photograph may give a more creative aspect.
-The second photo is a more correctly exposed of the same scenery and the colours are brighter and there are more details showing making the whole picture more interesting and more appealing.
-The third photo is underexposed. Too little light was coming through the lens and again many details are lost. Never the less i really like this photo because the trees and houses are in the dark and the emphasis is on the background which is really warm and beautiful.
-I found these photos using google search, they are not mine but they helped understands the concept of exposure.