How hard can it be to mess up? a couple little characters on the keyboard - "rm -rf /"... you may as well have signed your own death warrant
Just because software is stable, that doesn't mean that it's fool proof. Stable only means that they've done their best to strip out bugs from conflicting programs etc. It has no bearing on how the system actually operates.
As far as learning things on your own, be ready for a lot of learning, reading, testing and failures. Please Please Please use a testing server and not a production server for your learning. You don't want to be providing services to a customer if you're only testing things out.
Security is a huge concern. Have you ever used the shell console in Unix before? If not, do a search in google for "common unix commands". The CLI (Command Line Interface) is your friend. Once you know the basics of moving, copying, grepping, finding, deleteing and linking, then you'll want to get into shell scripting. Do you have any experience with Perl, CGI, PHP or any scripting lanugage? If not, you'll want to get your hands on an introduction to PERL. There's even some "books for dummies" series on BASH SCRIPTING (which is from the command line in Unix).
Get into forums involved in Unix and Shell. Google search will be a big help to you. You'll need to find books or papers on how to read logs on a server. How to close and open ports, permissions, file creating, more logging, and then you're a little closer to operating a server.
You hear people say "get a server a play with it" and while it's not what you want to hear, it *IS* the best way to learn things. You can read as many books and papers as you want, but until you physically are doing the process and seeing the results first hand, you'll not actually LEARN how to do it. Pick up a low end VPS server as it provides root access to you. You can use a separate boot on your personal computer too if you wanted.
Learning unix is like telling someone you want to learn Japanese! It's not easy, and if you're not using it on a regular basis, you'll forget it. Also, if you don't have someone around that you can practice it with, your learning curve is a lot higher.
Much like you probably didn't go to school to learn how to use Windows (much of it was click and trial & error), the same is said for a lot of Unix.
I can give you unix commands for various tasks, but until you understand the root of them, the commands aren't much help;
netstat -plan|grep :80|awk {'print $5'}|cut -d: -f 1|sort|uniq -c|sort -nk 1
That's not going to do you much good unless you first know what "netstat" is, and then how to use grep, what :80 is and what the final thing is for the output (in this case, how many people are looking at port 80, from what IP, and how many instances from that IP)
Grep, Find, SED, PS, Generic Unix Comands and netstat I use on a DAILY (if not hourly) basis when managing a server. Start with these.
"security" for the most part is just a singular word for good server management. Knowing how to upgrade programs and scripts will be half the battle. Keeping things updated is a big part, and then finding and eliminating trouble areas is the final part. This is all done in REACTIVE MANAGEMENT. If you want to be PROACTIVE, then you'll need monitoring scripts to help you out. Thankfully thousands of them already exist on the web that you can use freely.