I need to buy a nikon camera but I dont know what lens to choose
The AF Micro-NIKKOR 60mm f/2.8D focuses down to 8 inches and provides 1:1 magnification. This will be an equivalent of 90 mm so you will really be close up to anything that you are photographing.
http://www.nikonusa.com/pdf/manuals/lenses/AF/60mmf2.8AF-S.pdf
You can also try the 105mm Micro from Nikon and it focuses down to a foot, but with an equivalent 165 mm effective focal length with the D80, this will be up close.

A micro lens is what you need.
References :