Quick Question on the Difference between Longer/Sh

What is the difference in a Short and Long barreled telescope. I keep seeing models with 8" like the Orion XT8 that are 44 inche long barrels long, but then also see 8" models that only have 18 inch barrels. Some of the shorter ones even seem to have longer focal lengths published and that confuses me. Can someone explain how this works to me?
Is one better for one purpose or another than the other?

The shorter scopes with the longer focal lengths are compound scopes. The primary image from the mirror is magnified by a curved secondary mirror and this magnification is what gives it the long focal length. Here's a link to a quick explanation with diagrams. Also note that just about everyone of the telescope manufacturers have a section on their web sites that is dedicated to beginners. Google 'Telescope types' and take a look. The pictures are worth more than simple explanations.

http://www.wvp-consulting.com/astronomy/othertelescopes.html