Learn your terminal (or command line)
Enter stage left: the terminal (or command line, on windows). That window with strange white text on a black background. You might not see it, but every operating system has one - humming away in the background, just waiting to be used, but epic arcane skills are needed to navigate this bizarre and perhaps dated window into your computer.... or so it seems.
When you think of your computer, you will probably think of a GUI (a.k.a. goo-ey), with windows, a cursor, and perhaps a few buttons. GUIs make it easy for newcomers to easily find their way around a computer by referencing things that exist in the real world (e.g. folders and files, a floppy disk on the save button, etc.), but they can be inherently slower to use - especially for long series of perhaps repetitive tasks that stay essentially the same.
A terminal (linux and friends) or a command line (windows) is another view into your computer. It's a way of controlling your computer with text. Text that follows particular set of rules, that can be saved and repeated at will through the use of scripts. It's built on commands, each of which does one thing and one thing well. On their own they're mildly useful, but together they form a powerful framework that can perform almost any task. It's certainly different (and there's a little bit of learning curve, to be sure), but not as hard or arcane as you might think it currently.
A knowledge of the terminal or command line on your computer can be rather useful - especially so for those involved in computer science or technical support. How long would it take you to flatten a large set of deeply nested folders with a GUI? Or convert and recompress few folders worth of videos? Or even renew all your ssl certificates on your web server? All of these things can be automated through the use of a terminal or command line.
Even if you're just a casual computer user who's not into programming, it's still worth at least looking into. Perhaps it'll save you some time! Perhaps it'll save you from asking your friend where something is on their computer when you can't find it. Maybe it'll even save you if your computer suddenly decides it doesn't want to boot up properly. And you'll look cool doing it too :P (What better reason is there?)
If I've somehow managed to convince you to dive in and take up the challenge learning, then I'll end this somewhat different post with a collection of places you can go to get started.
- Linux Tutorial - Learn the Bash Command Line by Ryan's Tutorials - An excellent 13 part tutorial on the basics of bash and the terminal (Still useful if you use zsh for the basics at least).
- Computer Literacy 101 on linuxcommand.org - A linux terminal tutorial. Uses bash. Your prompt might differ, but the concept is the same.
- Using the terminal in the Ubuntu Documentation. Ubuntu specific, but again, the concept is the same. Read Computer Literacy 101 first.
- An Introduction to the Linux Terminal by Mitchell Anicas in the Digital Ocean Community - mainly aimed at servers, but still useful.
- Computer Freely - A guide to different Linux Distributions, how to choose one, and how to switch to using it full-time.
- explainshell.com - Enter a linux command on this website, and it'll tell you what each part of it does. Really useful for dissecting those long and complex one-liners.
- Explain a command - if explainshell won't do it, then this one will :P
- Linux Commands - A practical reference on pixelbeat.org
- Linux Terminal Command Reference by Alexio on community.linuxmint.com
- Linux Shell - Getting Started - A good whistle-stop tour and reference.
- Linux/BSD command line wizardry: Learn to think in sed, awk, and grep on Ars Technica
- Command line wizardry, part two: Variables and loops in Bash on Ars Technica