@gairsty http://www.linuxfromscratch.org/ really helped me get a grasp on things back when I was a geeky teen just getting started with it.

I'd also recommend these, since talking the terminal and related stuff digs up so much about the system as a whole:

* http://www.linusakesson.net/programming/tty/
* https://www.tldp.org/LDP/abs/html/
* http://mywiki.wooledge.org/BashFAQ
* http://www.catb.org/esr/faqs/things-every-hacker-once-knew/ (Stuff like why ASCII is laid out the way it is.)
* http://www.catb.org/~esr/writings/taoup/html/ (Focused on *why* UNIX programs are designed as they are.)