just the basics, as i have started using a router with dd-wrt loaded on it, and a NAS with debian on it (both done for me by a forum-member), and i don't want to just follow instructions blindly, but even understand what am doing or ought to do. moreover, it would be interesting to learn something new.
Start with installing Linux distro, I would prefer Ubuntu. You can either install in a
virtual machine or in a separate HDD partition and
dual boot with Windows (or
this) I would prefer dual booted Linux or a machine with only Linux ;-)
Then start with basic linux commands. File handling, users, permissions etc. Following important commands and operators come to my mind now :
|, <, >, >>, &, ack, awk, cat, chmod, chown, cp, mv, rm, export, find, locate, grep, kill, top, ps, sed, sort, tail, more, less, top, vim, vi, emacs, pico, whereis, which, xargs, sudo, su
Learn to use all of these and be good them. You should be confident to all of these. Then you can start learning scripting language to automate the task. You could learn about sockets, ports etc all networking related stuff. Just yesterday I myself wrote a
multi-threaded web server, works fine for my needs
You should definitely read this
book, it's a one of the must have books. It's written by Brian Kernighan and Rob Pike (Google about them if you don't know who they are). And
this also looks fine.
There are many things you can do, like networking, automation, shell scripts etc. pick one and be good in it ;-)
All the best!