Explaining what widescreen is and how it differs from pan & scan is good but you really need visual appreciation on what the differences are. I have been fortunate enough to borrow the following examples of some well known movies for your viewing pleasure. In each example, note how much information is actually lost - parts of the screen you never knew existed unless you watched the movie in the cinema or have the widescreen version.

Lord of the Rings: The Fellowship of the Ring: 20% - 45% of the original movie is lost when transferred to pan & scan
Pan & Scan	Widescreen
Pan & Scan	Widescreen
Pan & Scan	Widescreen
Pan & Scan	Widescreen

The Mask Of Zorro: 45% of the original movie is lost when transferred to pan & scan
Pan & Scan	Widescreen
Pan & Scan	Widescreen
Pan & Scan	Widescreen
Pan & Scan	Widescreen

Tomorrow Never Dies: 45% of original movie is lost when transferred to pan & scan
Pan & Scan	Widescreen
Pan & Scan	Widescreen
Pan & Scan	Widescreen