If you want the basics of encryption and a simplified look at AES encryption, here's a nice cartooned primer. If you know what your looking for, finding the key will be easier.
http ://www.moserware.com/2009/09/stick-figure-guide-to-advanced.html
Oh and just to make it weird. We used to use DES which was designed by IBM and code named 'Lucifer'. Its outlined in the graphic.