I've had some trouble doing specific things on Linux in the past because I didn't know some rather important commands that everyone should know. Here are a few of them (I'll list more when I remember them):
Ctrl Alt F1
this logs you out bringing you to login: prompt, similar to Ctrl Alt Delete in Window$, but more useful. Do this when a program fails to respond and you have no way of reaching a terminal. It removes the need for hard reset.
# /sbin/shutdown -r now
this restarts the computer from the terminal
# /sbin/shutdown -h now
this shuts down the computer from the terminal
$ ps -U $UID
this lists all running processes that you have started
$ kill -TERM ####
here #### is a process id number, this terminates a process; use in combination with ps -U $UID
$ cat file1 file2 file3 ... fileN > concatenatedfile
the easiest way to join files.
$ rpm2cpio name.rpm | cpio -id --quiet
extracts an rpm
Besides these there are things like cd (change directory), ls (list contents of directory), find -type f (find all files in a directory) find -type d (all directories in a directory), ln (make symbolic links), rm (remove files) rm -r (remove directories), grep (find lines in a file), cp (copy files), mv (move or rename files), chmod (change permissions), chown (change owner), mkdir (make a directory) ...
ok well, that's more involved I suppose, but I can tell you it's real useful when GUI fails
Here's a nice guide to bash (you don't have to learn shell scripting, just pick things that may be of use, and if you want to, learning bash is not too hard either)
http://www.linuxcommand.org/learning_the_shell.phpand burning CDs and DVDs from the terminal may come in handy too:
http://yolinux.com/TUTORIALS/LinuxTutorialCDBurn.html