What are specific lens's for?

I was just wondering what what different lenses are best suited for, for example, the nikon D5100 comes with two lens's a 18-55, and a 55-300, i know that the 55-300 is probably intended for zoom, but is that all, just how much you need to zoom? What should you use the separate lens's for specifically?

A lens is specific just for your need; they change the vision range. A zoom is a variable focal length lens, worst in quality but versatile

The point of a zoom lens is to 'bring things closer', just as you would do for your eyes by using a telescoper or binoculars. The bigger the number at the long end of the zoom (200mm, 300mm or more) the further you can 'reach'. For sports or wildlife at least a 200mm is needed, 300mm is better.

The word 'zoom' really means that you can change the degree of magnification without interchanging the lens, thus a 18mm to 55m is a zoom lens (but from wide-angle to slight tele), a 55mm to 300mm is a zoom lens, but a 135mm is a fixed tele lens (about halfway between 55mm and 300mm in power).

For portraits 55mm is suitable, or 70mm, but no greater.