The shutter speed of the camera indicates how long the shutter remains open to let the light through to the film or the digital sensor.
The number series for shutter speed in seconds are as follows:
30, 15, 8, 4, 2, 1, 2, 4, 8, 15, 30, 60, 125, 250, 500, 1000, 2000, 4000, 8000, 16000
In the above series, the numbers to the left of 1 second are whole seconds and to the right of 1 second are in fractions of a second. They are not expressed on your shutter speed dial as fractions because of space limitations but they are in reality fractions as follows:
30, 15, 8, 4, 2, 1, 1/2, 1/4, 1/8, 1/15, 1/30, 1/60, 1/125, 1/250, 1/500, 1/1000, 1/2000, 1/4000 ,1/8000,
Again, each number moving to the right in the table is half the value of the preceding number, and represents half as much light getting to the film or sensor as the previous number, which is the equivalent of one stop of light.
Slower shutter speeds will give a more blurred image and faster shutter speeds will help eliminate camera shake. A good rule to reduce camera shake is to use a shutter speed faster than the focal length of the lens in use. For example with a 100mm lens use a shutter speed of 1/100 of a second or shorter.
Most cameras limit the slowest shutter speed to around 30 seconds, however remote control units are available to extend the range of shutter speeds beyond 30 seconds. For Nikon cameras on of the best remotes is the Nikon Remote Cord MC-36.
Some high level cameras may give a shutter speed range higher and lower than those indicated above.
Sometimes you may want to deliberately cause blur in images. In capturing subjects such as waterfalls or flowing rivers it can sometimes enhance the image by using a slow shutter speed to cause the flowing water to have a velvet type look. A neutral density (ND) filter over the lens can assist greatly to use long shutter speeds and cause this blur effect. I have managed to create some very interesting effects using slow shutter speeds and ND filters..
When using longer lenses greater than 100mm fast shutter speeds are desired to help freeze the action, this is where high ISO capable cameras are great to give more capability to use higher shutter speeds.
The current day cameras have far greater capability and flexibility to provide more options in relation to giving photographers greater access to a wider range of shutter speeds.
So start being creative and try some long exposure images. Bear in mind that when using long shutter speeds and ND filters you will need to use a tripod and a remote release to help stabilise the camera.