getting started "boot the 'Live CD' "

Like several other linux Distributions, Ubuntu comes as a "Live" CD. This means that you can boot from the CD and run the Linux as though it was installed on your machine. the downsides are: performance asnd persistance (or lack there-of).

• Performance: Since you're running from the CD which is may times slower than the typical hard drive, the response of the system will be somewhat more sluggish than from a fully installed system. That said once booted it seemed to run pretty well to me...,
• Persistance: Any Changes you make to the settings of the operating system will be gone after the next reboot of the Live CD.

Issues aside, You can get a pretty good feel for linux by running the live CD.