This is a Magic Lantern guide by Simon Stafford who is a bit of a Nikon wizz and is involved at Greys of Westminster I think.  Excellent book as it really goes into detail about the camera rather than just about photography in general.  Keep it in my camera bag as it is a small field guide and it is brilliant for reference.

Stafford, S (2011)  Nikon D3100 Pixiq publishing.  New York