What do different lenses do?

I'm probably getting A Canon EOS Rebel T2i or A Nikon D3100. But I see their are many types of lenses that you can buy separately.
What are all these different lenses for and what lenses comes with the camera? Please explain, thanks.

You do know, don't you that the D3100 is the only one of the two that can use auto-focus when in the video mode?
This link will help you understand lenses
http://www.tamron-usa.com/...arison.php
The 18-55 mm lens that comes with most dSLR's is one that can shoot landscape, groups as well as head and shoulder shots (portrait)

Either camera comes with a basic 18-55mm lens, which is not bad for most basic shots.
Here's a link to let you see what different lenses can do.
http://www.nikonusa.com/...ength.html

Both cameras comes with 18-55mm lenses but the Nikon has a lens that can auto-focus continuous in video mode. Also the Nikon D3100 has full HD 1080p video mode.
If you are a starter both lenses are good…
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