Short bio: Computer Scientist, FOSS supporter (read more)
Tux Machines (TM)-specific
Learning UNIX is a seemingly daunting task, there are thousands of commands out there, each with hundreds of options. But in reality you only need to know a few of them.
I use unix quite a bit, usually either on one of our Linux servers, or on my Powerbook with OS X. And these are the 15 commands that I use most. If you can memorize these 15 commands, you can do quite a bit on a unix operating system, and add unix as a skill on your resume.
The 15 Most Important UNIX commands
1. man - show manual for a command, example: man ls hit q to exit the man page.
2. cd - change directory, example: cd /etc/
3. ls -