Your camera relies on the combination of aperture
and shutter speed to determine proper exposure.
If you have a wide range of shutter speeds,
you have more latitude in deciding what aperture
to use and what kind of pictures you can take.
If you have a limited range of shutter speeds,
or worse only three or four shutter speeds,
you might find that most of your shots are underexposed,
or the camera applies software techniques to
"boost" the available light by manipulating
the image captured, which usually results in
loss of image quality. So, even though you might
buy a 3+ Megapixels resolution camera, your
limited shutter speed range effectively diminishes
the image quality you obtain in capturing a
properly exposed picture (e.g. the camera might
have to use a higher ISO setting and introduce
noise in your picture). Bottom line: ensure
that your digital camera provides a full range
of shutter speeds ranging all the way from fast
(e.g. 1/1,000 sec.) to slow (1 sec. or more).
A Note on Shutter Speed/Aperture/ISO
To properly expose a picture, your camera needs to let in enough light to reach the film or image sensor (in the case of a digital camera). So, let's assume we set a fixed aperture (the opening of the iris in the lens that allows light in).
In a sunny situation, there's a lot of light, so a camera set on Auto mode will usually select a fast shutter speed (say, 1/125 sec. or 1/500 sec.) so the image sensor is exposed for only a short time to the light.
In a cloudy or dark situation, the camera on Auto mode will usually select a slow shutter speed (say, 1/30 sec. or 1/15 sec.) so as to allow the image sensor to be exposed for a longer time.
Basically that's how shutter speed works for a selected aperture. Usually, however, the camera on Auto mode will select different combinations of shutter speed and aperture to obtain proper exposure.
In general, the following applies: a small aperture means less light reaches the image sensor, so the camera needs to open the shutter for a long time; a large aperture lets in more light, so the shutter speed opens for a short time.
You can also set the image sensor sensitivity (ISO) to affect exposure. A high ISO needs less light, a low ISO needs more light for proper exposure. Common problem with current consumer digital cameras is that high ISOs introduce quite a bit of noise as to be mostly unusable, so don't get fooled by 'features on paper.'