This is a great tutorial website by Canon for anyone who needs a primer, brush up, or just wants to play around with how shutter speed, ISO, and f/stop all work together to create an image. The page allows you to manipulate settings of your DSLR, take a picture (complete with appropriate sound fx), and review the image. When you review the image there are text boxes instructing you on the settings you chose and ways to change the image if you want (underexposed, too much depth of field, etc).
Play with the camera controls found in the "Creative Zone" of an EOS Digital SLR. Here, you can really dictate the outcome of your photos and get the effects you want. Your shots will appear below where you can review, get feedback and compare the settings you used.