Makeuseof.com is an excellent site and I use it a lot. They have lots of useful information and resources, much of it available as downloadable pdfs. One of these is
An Idiot’s Guide To Photoshop
Have you decided to venture in the world of image editing? Decided, but don’t know how?
Photoshop can be quite difficult, if you throw yourself at it without preparation. You’ve probably got no clue how everyone gets that wizardry done, because you don’t know head from tail in that maze of buttons and filters!
Don’t despair, because MakeUseOf will be your guide in this intricate, yet magical world.
We’re proud to present An Idiot’s Guide To Photoshop, the starter’s manual for every Photoshop initiate to carry! This guide starts right at the very bottom, assuming no knowledge at all, and walks you through all basic aspects of the application. The guide even comes with three full pages of shortcuts, cheat sheets covering all the application’s possibilities!
You can download it from their site here: http://www.makeuseof.com/tag/an-idiots-guide-to-photoshop/