SB-900 for dummies

This flash is too much for me.

I need a for dummies style written reference giving me blow by blow guidance on how to use it in a range of light conditions and specific uses.

Any pointers would be hugely appreciated.

I don't know of anything written specifically for the SB-900. Oleg Novikov did a good starter article when the Creative Lighting System was new. It is available here. Nikon did a brochure with examples and how they were made, available for download here. They are both written for the SB-800 but the methods are the same. To find more tips and tricks, search the web for CLS rather than SB-900. One thing that is badly documented is the use of FV lock, not to lock the flash exposure but rather to give the eye time to open again after the measuring preflash. To get the most out of your flash, experiment as much as you can. 

David Hobby's Strobist is a wonderful source when it comes to understanding how to use small flashes well manually.

I use Mike Hagen "The Nikon Creative Lighting System", ISBN 978-1-933952-99-4.

It covers all the current Nikon flashes and their functions pretty well.  Not sure it worth the $40 price tag though.

YouTube, there are "how to" videos on just about any subject.