Shutter speed is one of two factors that determine how much light your camera's sensor is exposed to when you take a picture (exposure.) Consequently, shutter speed is one of the most important things to understand if you want to venture out of "green box" mode.
Controlling your shutter speed gives you more control over exposure and more control over creativity. The simplest way to begin experimenting with shutter speed is to put your camera in "shutter-priority" mode. To accomplish this, rotate your camera's control dial (indicated below) to "S" if you have a nikon camera like the D40 or "Tv" if you have a canon camera.
In shutter priority mode, winding the command dial (indicated below) will change your shutter speed and your camera will do the rest of the work to produce a correct exposure. As you peer through your viewfinder, you will see a number changing as you wind. That number indicates your shutter speed (it's not the number with the "f" in front of it, but the other one.) The number indicates the reciprocal of your shutter speed in terms of seconds. In other words, if you see a 60, then your shutter speed is 1/60th of a second.
There's lots more to say about shutter speed, but that's enough for one day. Try experimenting with it and see what happens. More on this tomorrow.
