Shutter Speed and Motion
The Shutter is a Curtain
that covers the camera's sensor until you push the Shutter Button and
then it opens for a specified length of time (Shutter Speed) thus
exposing the image sensor to the light from your image.
This is one of the three ways of controlling your Exposure Value (EV) and creating a well exposed photo. The more light needed for a proper EV the longer/slower the shutter speed. When less light is needed the shutter speed increases and allow less time for the light to hit the sensor. (See Pocket Guide under Motion/Shutter Speeds)
the Shutter Speed
the less movement in the photo (freeze the action
The Slower the Shutter Speed
the more movement in the photo (blurred image and showing movement).
To control the Shutter Speed you can adjust the Aperture (open it up or close it down) or adjust the ISO (increase ISO increases Shutter and Decreasing ISO slows the Shutter). (See Pocket Guide Aperture and ISO).