A content management system (CMS) is critical to the success of almost every website. A good CMS allow webmasters to add new page, modify existing pages with out knowing HTML or Web Server related stuff.
With CMS even CEO of the company can update the web site from anywhere by loging into CMS admin area. CMS also allow different level of users. You can make a user editor, so he can add news or atricles to the web site. Adding new pages is easy as creating a page in MS Word.
You can see DEMO of various Open Source CMS software at www.opensourcecms.com
Some of the popular CMS are