I have given some basic courses on Unix for people working at Helsinki University of Technology. Together with Timo Larmela, I have written a book (in Finnish) about using Unix; the book is Johdatus UNIXiin (published by Otadata).
I have also authored or co-authored several Unix-related guides and Web documents in Finnish.
My experiences with Unix include variants of BSD as well as AIX, HP-UX, and DEC OSF. As regards to the question "which Unix is the real Unix?", I have no strong feelings.
On the Web, there are at least three rather good and extensive sources of information about Unix:
manpages, I'd say (unless you really need to find machine-specific information). Note: The require you to register, but after that you can bookmark a page through which you can access the information conveniently.