A great educational resource for anyone wanting to learn basic DSLR funcationality and exposure is the CameraSim.
CameraSim is a free online DSLR simulator (ipad and iPhone versions are paid) that allows you to change ISO, aperture, and shutter speed in the simulator and then shows the results of those changes.
Great for those that are hoping to learn the basics. Check it out at
http://www.camerasim.com