People who are new to photography or exercising control over their cameras (e.g. new DSLR owners) find that it’s not as easy as it seems. And they think it should be, after all, this is 2009. It’s not like they were Lartigue in 1900.
Sometimes, they don’t want to read dry text, so I point them to interactive tutorials or visuals on the web.
Tamron offers a Focal Length gadget
Tamron offers a Depth of Field gadget
Craig Hickman offers Camera Demo, a gadget that lets you play with ISO, Shutter Speed, f/no, Light Level, Exposure Compensation and different modes – P A S M and full Auto
PhotonHead has some simple pages showing tables of Shutter Speed, f/no and what a “stop” means