The second post asks a lot of very complex questions:

I started with Unix in 1991, moved on to Linux and SunOS / Solaris after that. To this day I'm still learning new things. I was in the Navy back then - it was a pretty hostile environment for noobs : )

Reading. Curiosity. Experimenting. Breaking. Fixing. (With a healthy dose of impossible deadlines) That's how I learned.

Unix System V - A Practical Guide. If you can pick this book up anywhere, I would highly recommend it. It was published 15 years ago, but unix being what it is, it is still as relevant today in the Linux world as it was back then. It will teach you all about the more useful core applications you can expect to have available, what they do, how to use them, and so on.

Alternatively any kind of Linux systems administration book will do the trick. Absorb any of these and you'll know on your own how to find the answers to your questions. Take a look in /bin /usr/bin /sbin /usr/sbin and see what's available. Try running everything you come across or look up the man page for it.

It WILL take you YEARS to learn this stuff. There are no shortcuts unfortunately.