Exposure is the combination of aperture and shutter speed. Aperture (measured in f-stops) determines the amount of light that will enter your camera. Shutter speed (measured in seconds) determines the amount of time that the shutter will stay open to allow light to enter.
Shutter speed is how fast your shutter opens and closes to take a picture on your camera. Shutter speed also has a lot to do with exposure. The higher the shutter speed (1/2000 example) the less light.
You can adjust the shutter speed of Canon EOS cameras so there isn't a set shutter speed.
Fractions of a second. 1/8 1/16 1/36 1/400 1/4000
The shutter speed setting controls the picture exposure, or how dark or bright the picture will be. Wikipedia has some very good information on shutter speed and aperture.
It doesn't necessarily inprove your picture. The higher the shutter speed, the less light, also the blur in a photo. A higher shutter speed will freeze a photo. A lower shutter speed will blur most motion and will increase chances of blur.
Shutter speed has a lot to do with your overall exposure. A higher shutter speed will decrease the light a lot. I was in best buy playing around with a camera and turned the camera shutter speed to 1/4000. After taking the photo, the preview was black. I realized it was because of how much higher I increase my shutter speed. Shutter speed also affects motion in a photo. A higher shutter speed will freeze all action in a photo a will less likely have a blur to it if you have a shaky hand. A lower shutter speed lets in more light while the shutter is will opened so the entire time that the shutter is open, the camera takes in all that light. Increasing chances of blur, you can also use this for crazy, funky effects! If your taking a picture of a waterfall with a low shutter speed, your gonna get a blur, which can typically look pretty epic sometimes too.
The highest shutter speed available to you will give you the darkest exposure, while the lowest shutter speed available will give you the brightest exposure
Slow shutter speed - keeps the shutter curtain open for longer periods of time, e.g. when you shoot at night or in fading low light. Fast shutter speeds are used to capture action or when scene you are trying to shoot is well lit. In this case the shutter opens and closes in a fraction of a second!
Shutter speed is how fast your shutter opens and closes to take a picture on your camera. Shutter speed also has a lot to do with exposure. The higher the shutter speed (1/2000 example) the less light.
1/250-1/500
All cameras have multiple shutter speeds and depending the mode your camera is (Manual, Auto, etc...) the camera will choose what shutter speed it thinks will be appropriate for the picture. And most cameras will also not tell you the shutter speed you used, while some will.