These stubby-looking scopes are often found in ads in the backs of astronomy magazines. A lot of places are selling telescopes called dobsonian telescopes. These are actually newtonian reflectors on a very sturdy, inexpensive mount based upon the design of John Dobson. There are a lot of numbers thrown around when talking about telescopes. The most important criteria when choosing a scope is aperture .
Aperture is the diameter of the opening that lets light in the front of the scope.
Bigger is better, for two reasons. The main reason for needing a telescope to see objects in the night sky is that they are too dim to see without a telescope. In non-technical terms, the telescope takes the light that falls on its mirror or lens, and squeezes it so that the light fits through your eye's pupil, much like a funnel catches more rain than a test tube. The second reason why bigger is better has to do with the nature of light itself. Without getting into physics, the larger the aperture of the scope, the more detail can be seen in its image.