Some points to consider in your buying decision are portability, ease of use, cost, your observing goals, aperture, telescope designs, telescope mounts, and computer technology. A telescope with a large aperture gathers more light than one with a small aperture. Images will appear brighter in the telescope with the larger aperture under the same magnification. Go for as much aperture as you can afford and handle. Magnification is determined by dividing the telescope's focal length by the eyepiece's focal length in millimeters.
Magnification is changed by using eyepieces of different focal lengths.
Along with buying a telescope, a good astronomy guidebook is highly recommended. This is an excellent introduction to observing the night sky.