hello, fellojello!
You can find introductory tutorials with a google search (intro to unix).
But you can start by browsing the unix.com forum's very own:
https://www.unix.com/answers-to-frequ...tutorials.html
That would be a good start.
Apple has added some Mac specific commands and functions to what at one time was FreeBSD (er something...) and this Apple modified version of Unix is currently referred to as Darwin, which is available seperately without the Mac GUI.
FreeBSD lives on, of course, and is a fine Unix implementation in it's own right.
To get an idea of just what Unix flavors there are, and when... check out:
http://www.levenez.com/unix/