It's all a matter of what you want... telephoto lens (>70mm) for distant subects, wide angle (<28mm) for wider/larger subjects; "Normal" lenses (30-70mm range) for every day shooting; Portraiture 85mm and greater...
I tend to disagree with this. Photography is not inherently an artform. It's a technical skill. The selection of lenses and how you use them is merely a selection of the means to reproduce various aspects of something already existing.
In almost every other form of art there is a form of creation and/or recreation. If I were to paint or sculpt an apple, I have to create it by blending paints, or carving wood, or chiseling stone, or even creating a cad file and printing it on a 3D printer.
If you're to photograph an apple, one must first have an apple to photograph. Then you can apply your fundamentals in science (how light reflects/absorbs, how the sensor captures light, etc.), your technical skills (how to light the scene and work the camera), and artistic flare/foundations (composition, rules, color theory) to capture the light. However, the image you create can absolutely be art.
Does he want to know how to use a lens ? Does he want to have a list of available lenses for his system ? Does he want to have lens recommendations ? etc
he doesn't know how to go to any lens manufacturer's website and see a list of lenses they offer that are, shockingly, categorized by: this type lens for this type shot sorta thing.
for example, nikon categorizes their lenses as such:
Travel and Landscape Lenses People and Events Lenses
Sports and Action Lenses
Close-Up (Macro) Lenses
Special Purpose Lenses
Go look at some photos on Flickr -- a large number of these have EXIF information showing not only the focal length, but the aperture & shutter speed as well. You might start to get a feel for how people choose to use these things to create the "look" they want.
Me thinks you are getting a little ahead of yourself. Once you learn all the fundamentals of photography you will never ask is this a good lens for this or that, you will know based on physics and desired results. That said, if you are looking to buy a new lens, why not go the other direction and decide what you want to photograph and we can point you in a general range?
It's a simple newbie question ... what one doesn't know, one doesn't know how to ask.
John and everyone answered it.
The first link Keith listed is what I was going to post ... just in case you peruse over it too quickly here's the summary in the middle of hte page .. use as a rule of thumb
The following table provides an overview of what focal lengths are required to be considered a wide angle or telephoto lens, in addition to their typical uses. Please note that focal lengths listed are just rough ranges, and actual uses may vary considerably; many use telephoto lenses in distant landscapes to compress perspective, for example.