undex unix :
man [your shell]
I personnaly definitely prefer ksh whenever available ...
man ksh on an HP box gives you the best book ever written about scripting )
UNIX in a nutshell is indeed a vital book, but not for beginning scripters. it's a reference book. i can't recommend a scripting book tho, because i'm looking for one myself.
A good starting book is "A Practical Guide to the Unix System" by Mark Sobell, which covers the basics of Unix along with scripting in the three standard shells (Bourne, C, Korn). Also invaluable is the "sed & awk" book by O'Reilly to get comfortable with sed, awk and regular expressions.
Since I prefer ksh, I would definitely recommend Learning the Korn Shell by O'Reilly. I tried learning with Unix in a Nutshell, but like DBAtrix I see it more as a reference book.