UNIX is a terrible, kludgy, insecure piece of junk. It just also happens to be the best OS for small to mid-scale computers that is available.

UNIX consists of a kernel, which is most basically device drivers for the screen, keyboard, disk(s) and whatever other hardware is present in the system, and numerous applications and utilities.

I recommend the 'man' command very highly to all novice UNIX users. It's very important to experienced users too, but as one progresses up the learning curve it becomes more and more of a last resort. Because 'man', quite frankly, is terrible; but again, keeping in the spirit of UNIX, it is one of the best on-line help systems available. The writings are unfailingly obtuse, the subject is never covered adequately and examples hardly ever have anything to do with what you would want to use a command for. But it is there, and it is much, much better than nothing. Try 'man man', 'man intro' and 'man -k unix' for starters (these are not guaranteed to produce valuable results on all systems, but they should give you an idea of what's available and how you can expect it to be represented).

In this author's opinion, the power of UNIX lies in it's true interprocess communication, control, and file redirection that really works. As UNIX considers almost every object to be a file, this last point is really incredibly powerful. While we can go on for years studying the nuances of perl, awk, sed or whatever else fits an application need, we will ultimately find that >, <, | and & empower the weakest little commands to work together to accomplish extraordinary things. Learn these tokens. If you know them, learn them better. Many would argue that the power of UNIX lies in regular expressions, but your author would reply that regexps are actually application dependant, as standard as they may seem, and while they are truly wonderful (navigating by wildcards is a great way to save keystrokes as one of the simpler representations), the pipes, the redirects and the concept of foreground and background are, in this authors opinion, the features that demonstrate the power of the UNIX philosophy and therefore what sets the OS apart. I was happy when Linux gave us a free as in beer and as in liberty kernel that runs on commodity hardware and supports the GNU userland. I've always admired the BSDs but didn't appreciate their userland. Dragonfly has me looking at them very hard today; as has the intrusion of systemd. Devuan may keep me in Linux; I'd keep you posted iff there was evidence you cared.