• What is a shutter?.....A shutter is a device that allows light to pass for a determined period of time, for the purpose of exposing an electronic sensor to light to capture a permanent image of a scene. 
• "Shutter speed" then refers to the length of time that the shutter is open for.  A slow shutter speed allows more time for light to enter- giving you more light.  A faster shutter speed does not allow as much time to let light it- giving you less light.
• If we were to use our eye example again, think of the shutter as your eye-lid.  Shutter speed refers to how long your open your eyes for.
• Shutter speed also controls how motion is captured.  If you capture a moving subject with a fast shutter speed, it will freeze the action- giving you a crisp, clear image.  If, however, you photograph that same moving subject with a slow shutter speed, your subject will appear blurry. 

Shutter speed controls:

• - Exposure (how much light is let in)
• - how MOTION IS CAPTURED