Shutter speed is exactly what it sound like, the speed at which your camera opens and closes the shutter over the lens, the speed you choose will expose the picture to light for diffenert amount of time affecting the exposure of the shot. In normal conditions most will increase the shutter speed for larger apertues to keep the picture balanced.
Using a fast shutter speed is a great way to freeze action shots, a key moment at a sporting event or pictures of rain drops as they fall for example. Slowing the shutter speed down obviously lets much more light in, so it is usually a tecnique used in darker places or at night time. How ever using a slow shutter speed can also help you create movment within your shots, either placing your camera in a stationary position to show a subjects movement or moving the camera with the suject bluring the backgroud, this is called panning.
As with all new tecniques pratcice makes perfect so try different shutter speeds and see which results you like, if you need ant advice just ask and we will post you questions in the talking points area for other to share their views.