They contribute a lot to the cost of the camera so specifications vary considerably. The most obvious lens parameter is zoom range. It is very convenient to be able to take wide angle and telephoto shots with the same camera. 3X optical zoom is good, but fairly expensive. Cameras with fixed focus lenses tend to be easier to use and smaller.
Some cameras also have a digital zoom feature.
It does not capture more detail. Digital zoom can be used to extend the optical zoom range, but always check the optical zoom range, this is what really counts. Try the zoom in the store where you buy the camera to see if you like the range. Some digital cameras do not have good wide angle operation because it is hard to make a wide angle lens for a CCD sensor. If you care about taking pictures in low light look at the maximum F-stop your camera can support.