I have the "Learning Unix for Mac OS X" by O'Reilly. It is a well written book, that I purchased mainly out impulse and curiousity. It answers the questions that you ask, but is not a detailed investigation into Unix. What I would recommend would be to go to: Learning Unix for Mac OS X and check out the table of contents, and look over the sample chapter.
Then if you need more information, then look into: Unix in a Nutshell
That goes into a lot of detail and is an excellent reference.