Shutter speed controls the duration, or, for how long the quantity of light entering the lens, is allowed to act on the film/sensor. Hence shutter speeds also control exposure. But what else do shutter speeds do?
Shutter speeds play a very important role in creating sharp images. As a general rule, faster the shutter speed, greater the image sharpness (because there is less chance of camera/subject movement during the brief exposure time). Shutter speeds can also be used to create movement in our two-dimensional images. This is of course done using slow shutter speeds. Here are some examples of the effects of using fast and slow shutter speeds.
Aperture: f/3.2 Shutter speed:1/500sec
Jog Falls. Picture courtesy: Vinayaka Seetharam
Aperture: f/11 Shutter speed: 2.5sec