The following list of commands is not comprehensive. It is just meant to be a quick introduction that you can print out and paste to the wall next to your computer. To get documentation on any GNU/Linux command (most of these are usually GNU), just type man [command] in a terminal. To learn how to use the man command, type man man in a terminal.
An alternative to the man command is the info command. To learn how to use info, type info info in a terminal.
An introduction to some of the commands is below. To print out these pages as a reference, you can visit the print-friendly version.