What is shutter speed?: the time for which a shutter is open at a given setting.
Shutter affects pictures in two ways. The longer the shutter is open (the slower the speed) the more light you get. The more light you get the less noise you have as it evens out the random emission of photons from a lightsource. (Allows writing with light) The quicker the shutter the less chance there is of a subject moving so there's more chance of capturing a sharp image where motion has been stopped.
Shutter speed of 10 seconds
Shutter speed of 5 seconds
Shutter speed of 8 seconds
Ghost image: 5 seconds in shot 5 seconds out of shot