Not about how to play them, but about the terms associated with them. For example, I don't know what things like "pitch blend" are, or what is the difference between the various pickups or how the selection of wood for the fretboard or body makes a difference to the sound. As an add-on, it would be nice if the source also covered the different types of sound-modifiers (I know there are distortions, overdrive pedals, wahs, reverbs, but what else? The local guitar shops here aren't the knowledgeable)...
Many thanks in advance!
EDIT: http://entertainment.howstuffworks.com/electric-guitar.htm Something like this, maybe, but a little more advanced?