What Is A Content Management System (CMS)?
A content management system (CMS) allows you to make updates to your site content without needing to modify the source code.
Implementing a CMS
Many hosting services offer a 1-click install solution to installing popular content management systems. The simplest to implement content management systems I've found is CushyCMS.
CushyCMS just needs to have FTP access to your server and you simply specify which files you would like to modify with it and then apply a class to the sections you want to edit.