12.04 manual

Getting Started with Ubuntu 12.04 is called a "comprehensive beginners guide for the Ubuntu operating system," but may also be "suitable for all levels of experience" -- looking through it, I've already picked up a few tidbits that I didn't know before.

The manual includes installation instructions, tips on using "the Ubuntu desktop" (Unity), info on software management and troubleshooting, a "Ubuntu for advanced users" section, and more. You can download it in .pdf form from the Ubuntu Manual Project site, and either save it for future reference or view it in your web browser.