Lenses can be confusing due to all the number values tied to them. For example here is the lens information for the one that came with my D3100
18-55mm f/3.5-5.6 AF-S DX VR Nikkor
This can be pretty daunting for a newcomer to camera lenses. Lets break each part down and explain it piece by piece.
18-55mm This is the focal length of the lens. We can see it has a telephoto range of 18mm to 55mm so it has some “zoom”. If it was just 35mm listed it would not have any adjustment on how close or far you could see the object through the view finder. The higher the number the closer you can see the object through the view finder.
f/3.5-5.6 This refers to the aperture of the lens. This relates to how much light gets let into the sensor when taking a picture. The smaller the first number set the more light gets through, the larger the later set the less light gets through. This lens has a range also of 3.5 to 5.6. You can adjust the speed of the shutter between these values to adjust the amount of light coming through. If it was just a single value like f/5.6 then you can not adjust it on the lens and you only get the option of 5.6. This is also refereed to as f-stop. Going from 4.5 to 5 is one f-stop.
AF-S This is the lens type. We can tell that it is a Auto Focus lens. See your manual for which types of lens your camera supports. Some require motors in the camera body while others such as this one have it built into the lens itself.
DX These are lenses which only cover the smaller sensor of DX digital cameras. DX lenses have reduced capacity compared to regular lenses or “full frame” lenses. Typically only very high end cameras are full frame.
VR This means Vibration Reduction. This helps reduce the vibrations to get you a clearer picture.
Nikkor This is the manufacture of the lens.