Zoom lenses on digicams work much like the ones on camcorders. There are two buttons. One lets you zoom in, increasing the focal length and narrowing the angle of view, while the other lets you zoom out, widening the angle of view. The optical zoom is a true zoom which uses the whole of the CCD unlike digital zoom, which is a mere crop of the central part of the CCD, making up the image of the central pixels of the CCD only.
Optical zoom lenses on digicams are usually non-interchangeable, which means that you have to choose a camera with a zoom range that suits your sort of photography.
Zoom lenses on digicams usually range from 35 to 70mm, which is sometimes called a standard zoom, or they may be anything between 28 and 135mm or more, which gives you much more versatility and a much wider range of coverage.
One of the best things about a zoom lens is that you can actually change your angle of view without having to move about much. This can be convenient when you don't have space to move backwards and still want to capture the whole of a scene. or when you want to react quickly to photo opportunities and want to zoom in on the action to isolate it from its surroundings.