Shutter speed is a setting on your camera which controls the length of time the shutter is open, allowing light through the lens to the sensor inside your camera. Shutter speeds can go from very small fractions of a second, to several seconds long on most cameras.
So why would you want to change it?
On a very bright day when there is a lot of light, if you allow the shutter to be open for too long then too much light will get to the sensor. When this happens you end up with pictures that are very pale and almost all white. This is known as being Over Exposed.
Let’s say, for a simplified example, that to get a perfectly exposed image on a bright sunny day, ignoring all the other camera settings, that you need the shutter to open for half a second. This half a second allows just the right amount of light through to the sensor to get a well exposed imaged.
Now, as the day goes by and you get to the evening, there isn’t as much light about. So if you took a picture and your shutter speed was still set at half a second you would end up with a very dark image, or an Under Exposed image. This is because not enough light got through to the cameras sensor in that half a second. So in order to compensate against lower levels of light, you would need to keep the shutter open for longer.
You can see an example of under and over exposed images here.
This may seem straight forward enough, but the longer the shutter is open, the more chance there is of ending up with a blurred image. The slightest of movements while the shutter is open will register as a blurred effect. Sometimes this can be the desired effect, but most of the time you want a sharp image. Using a tripod, sitting the camera on a solid object like a wall or the floor or holding the camera against a solid object like a big tree or wall can help reduce the chances of getting blurry images.
Most digital cameras will have a fully automatic setting where it decides what settings are best, so all you have to worry about is pointing the camera in the right direction and pressing the button. This may be the mode you use all the time, but it’s well worth experimenting with these settings yourself to see what effect they have. Once you start to understand these settings and what they can do to your image you will open up a whole new range of photographic opportunities and much more creative and pleasing photos.