My disclaimer, remember I am a total rookie learning as I go. These are just my notes to help me become a better photographer and maybe help others along the way.
Shutter speed is the amount of time your shutter stays open and allows light to hit the image sensor in our digital camera. Shutter speed is measured in seconds, usually in fractions. Don't freak out, the fractions aren't difficult to understand. :) The bigger the denominator (the bottom number on the fraction) the faster the shutter speed. The smaller the denominator, the slower.
To freeze action in your photography you will want to use a faster shutter speed, and slower to cause blur (movement). Examples of times to use higher speeds would be to catch an action, like your child playing baseball and wanting to freeze some movement. Or if you want to see the water of a waterfall to look all soft and marshmallow like use a slower shutter speed, with a tripod. A tripod is suggested since anything below 1/60th of a second might show some camera shake. The picture of my daughter's feet on the potty is a good example of this. I wasn't trying to catch movement, but I was trying to allow a lot of light on to the image sensor since we were in the bathroom with little natural light, and I did not want to use flash. Some cameras offer REALLY slow shutter speeds, like a whole second to several, and even a setting called "B" or "Bulb". The Bulb setting allows you to leave your shutter open as long as you want to.
Slow shutter speed is usually 1/60th of a second to 1 second. Long shutter speed is considered 1 second or longer. Fast shutter speed is considered to be 1/500th of a second or faster. As you experiment with these different speeds in manual mode, be sure to keep an eye on the little ruler mentioned in my earlier post. This will ensure you have correct exposure. If you have a faster shutter speed, allowing less light in, you will have to compensate with a lower f/stop number, bigger aperture. Shutter speeds increments about double with each setting, examples would be 1/1000, 1/500, 1/250, and so on. This is good to know since aperture also doubles with each stop. So, if you want to change your shutter speed, but want to keep close to the same exposure you can adjust your aperture. This works both ways, if you want to change aperture (change your depth of field) then either open up aperture and lower shutter speed for similar look or go the opposite way.
Here are some guidelines from www.photography.about.com
The speeds listed are the needed speeds to freeze the action under normal conditions. If you want to blur the action, decrease the shutter speed. To adjust for a very fast situation, increase the shutter speed.
Football - 1/400
Baseball/Softball/Hockey - 1/350
Kids Running - 1/350
People Jumping - 1/250
Golf Balls - 1/3200
Water Splashing - 1/350
How does shutter speed effect focal length? If you are using a lens with a longer focal length you will want to use a shutter speed that is faster than if you are using a shorter focal length. If you are using a focal length of 50mm (which is what I use most of the time) you will want to make sure your shutter speed stays above 1/60th of a second. Then if you are using a longer focal length, like a lens that is 200mm, you will want to use at least a shutter speed of 1/250th of a second. Notice the denominator in both examples is bigger than the focal length. A general rule is to use a shutter speed that is 1/(focal length number) of your len's focal length. However, if your lens has image stabilization, you can use a lower denominator in the shutter speed and should be able to get your shot. Image stabilizers in your lens should allow you to go down in speed by about 8 times lower than the general rule.
A great site to check out for more information on shutter speed, and some GREAT examples of being creative with shutter speed is http://www.diyphotography.net/shutter-speed. There is a picture of stars and stationary objects that is so cool. I am going to have to try this one night, loved it!!!