Once you have the ISO image burned to a CD, just pop that CD in your CD-ROM drive and restart your computer. When your computer starts, it should boot from the CD.
On start up, the Linux distribution will try to detect your hardware -- everything from the video and sound cards, the network card, and even wireless. How well or badly a Live CD does this depends on the Linux distribution and the age of your hardware. Usually, it will detect everything. Wireless can be tricky, if only because some Linux Live CDs don't include wireless drivers.
From there, you can fiddle around with Linux to your heart's content. You can use the bundled software, work at the command line, and change the look and feel of the user interface. But remember that the Live CD version of a Linux distribution will start and run slower than one installed on a hard drive. That's because the software is loaded into memory and anything else is read off the CD which takes time. But you get a good idea of what Linux is like and what it can do.