I'm a fan of Take Control of the Mac Command Line with Terminal, by Joe Kissell. It's a $10 ebook that is specifically designed for beginning command line users on Mac OS X. I think it's exactly what you asked for. I find many O'Reilly UNIX books to be frustratingly opaque for the beginner.
Book blurb from the above link:
If you've ever thought you should
learn how to use the Unix command line
that underlies Mac OS X, or felt at
sea when typing commands into
Terminal, Joe Kissell is here to help!
This 111-page ebook will help you
become comfortable working on the
Mac's command line, starting with the
fundamentals and walking you through
more advanced topics as your knowledge
increases. And if you're uncertain how
to put your new-found skills to use,
Joe includes numerous real-life
"recipes" for tasks that are best done
from the command line.
Disclaimer: Though I wrote a Take Control book seven years ago, I have no financial interest in Joe's book.