This is a simple example of the result of 2 different flash placements--on and off camera. The shot at left shows a more natural light and could easily be mistaken for a shot taken on a sunny day. The other shot, using strictly on-camera flash, looks dull and lifeless, however, unless you're a photographer, you probably wouldn't even realize why.
The message here: get your flash off. Your pictures will have more depth and natural appearance.