Shutter Speed :

The shutter speed is the amount of time for the shutter to open and close, the faster the shutter speed the less amount of light will be let in  during the time taken for the image.

Example:

Above are two examples of the same photograph set up but taken with different shutter speeds.  Both photographs were taken with an aperture with F5.7 so that I could see the full effect of only changing the shutter speed.  The first photograph with a slower shutter speed produced an image that was over exposed and had too much light in it,  this happened because the shutter was open for longer so more light was being let into the image leaving it over exposed.  The second photograph however had the shutter open for less amount of time and produced an image that isn’t over exposed as not as much light was being let in.