Whoa, hang on! Reinstallation of the OS is, generally speaking, a last resort, and a major one at that. You can get that OS tuned up and running more quickly and smoothly with a System utility like
Titanium Software.
However, if you're determined to reinstall the OS, yes, put the cd or dvd in the drive slot/tray and reboot, holding down the C key immediately after the 'bong'. You need to do and Archive & Install in order to preserve all your applications and files that are not part of the OS.
Make sure you have sufficient hard disk space, because A&I will create a Previous System folder, just in case you need it later.