Examples for many Unix concepts and commands from the University of Edinburgh. This is a really good place to start!
Web resources to help you learn the bash shell
Help on how to check your account size and some basic commands to help you compress, archive and remove files and directories
Both the man (for manual) and Info pages provide information about the system. Man pages are typically geared to specific commands or files, while Info pages give information about an application as a whole.
You're typing along, you enter a command, and now your machine is frozen! This will help!
Are you hogging the processor? Here's some info on how to make your processes play nice.
“I accidentally pressed a button and all of my work disappeared. Help!”
Most of the window managers give you multiple (4 by default) virtual desktops. Each desktop is an independent workspace, so if you go to the second desktop, it will appear as if all of your open programs are gone. Don't worry, though, you can go back to using them by switching back to virtual desktop 1 or generally clicking on the image of a different desktop on the panel.