Nikon 70-300mm f4.5-5.6G ED IF AF-S VR Nikkor Zoom Lens?

Could you please exp line
what is 70-300mm?
what is f4.5-5.6? How to under stand this zoom distances (tel me the answer in feet)

The 70-300 is the focal length of the zoom; or how much magnification it has. The 70mm end magnifies less than the 300mm end.

There's no feet relationship per se. You can zoom in to 70mm or out to 300mm regardless of whether your subject is 20ft or 200ft away. The 70mm end would give you more of a photo with your subject and the background, the 300mm end would give you a photo of a closeup of just your subject.

Look at this website for a comparison of the different zoom lengths, which should give you an idea of the magnification for each:

http://www.althephoto.com/concepts/lenses.php

The numbers f/4.5-5.6 are the maximum open aperture the lens has. The aperture primarily regulates light going through the lens, and secondarily, controls the depth-of-field. The two numbers indicate the maximum aperture at each end of the zoom. So the lens is f/4.5 at 70mm and f/5.6 at the 300mm end.

If you are not familiar with aperture or depth-of-field, here are two references:

http://www.althephoto.com/concepts/aperture.php

http://www.althephoto.com/concepts/dof.php

AF-S means the lens auto-focus system has it's own internal focus motor. Since Nikon's entry level cameras, such as the Nikon D3000/D3100, D5000/D5100, D40 and D60 do not have a focus motor built into the camera, they need AF-S lenses to focus.

Finally, VR means Vibration Reduction, a mechanism in the lens to help prevent "camera shake", which is a result of the photographer not holding the camera steady. This can become significant with telephoto lenses such as this, and VR helps in taking a good photo.