16. man

Gee I wish some of these programs had a manual so we can see some more information about them. Well luckily they do! Aptly named man pages, you can see the manuals for a command with the man command.

$ man ls

Man pages are manuals that are by default built into most Linux operating systems. They provide documentation about commands and other aspects of the system.

Try it out on a few commands to get more information about them.