can anyone please tell me what the numbers 18-55mm mean? all of the different lenses have them but what exactly do they mean.
neil

It is the focal length of the lens, that is the distance between the front element to the focal plain of the film or imaging element or chip. Lower numbers yield wider angles (and are this "wide angle" lenses) and higher numbers yield narrower angles and greater magnification and are called "telephoto" lenses Based upon the size of the film or chip or other collecting device, this focal length will provide different angles of view, which leads to different apparent (as opposed to actual) magnifications.For example, on 35 mm film a 50mm lens is roughly equivalent to the angle of view of the human eye (and is therefore often called a "normal' lens). On many common D-SLRs, the collector is smaller than 35mm, and thus a lens with a focal length of 50mm renders an angle of view more similar to a 75mm lens (on 35mm film) and it thus gives apparent magnification greater than the same 50mm used on 35mm film. Of course, on collectors larger than 35 mm film (in medium format cameras such as the Hassleblad and larger) the reverse is true.
Based upon what size collector you are using, a zoom lens (that is a lens with a variable focal length) like the 18-55mm will go from wide angle to either slightly above normal, or small telephoto.

John