Are you new to Ubuntu Linux? the GUI interface may be easy to learn, but command line interface may little bit difficult to learn without proper guidance.

Ubuntu help documentation provides basic commands like File and Directory Commands, System Information Commands, Executing Commands with Elevated Privileges, Cutting and pasting.

Fosswire.com provides Ubuntu cheat sheet, where commands are categorized into Privileges, Display, System Services, Package Management, Network, Special Packages, Firewall, Application Names and System.

ubuntuguide.org a Ubuntu wiki, provides complete information on Ubuntu Linux operating system with command line examples.

Rute a massive online book for system administrators, which contains commands and guidance.

linuxcommand.org contains basic BASH tutorials, including BASH scripting.