What effect does the shutter speed have on the image?

Good question.
Shutter speed is how long a photo is exposed.(if your talking about in video/film how long each frame is exposed)

So if u have a low shutter speed the more motion blur there will be.

High shutter speed will do the opposite. So at high shutter speeds it will freeze the action.

Look at this photo
http://upload.wikimedia.org/wikipedia/commons/b/b2/Windflower-05237-nevit.JPG

the spinner is moving at the same speed in each photo the one farthest to the left is a higher shutter speed and to the right is a low shutter speed.

In Video/film

what i just told u holds true. The effects that i just talked about appear on each frame of the video.

So high shutter will but jittery and choppy (often used on purpose)

(This may also help)

The higher the shutter speed the less light enters the camera.
This means that in low light if u set the shutter speed high the camera will compensate most likely by making the ISO(sensitivity of sensor asuming its digital) this makes the image poorer quality. higher and the aperture bigger making the depth of field more shallow(if u don't know what depth of field is look it up) But that's just what the camera will do automatically if its set up that way and it needs more light.