There is a wide range of CMS‘s available for use. Some of them are free like Joomla, WebGUI, Bricolage, Mambo and some of them are commercial ones like Bitrix, Drupal, etc. Joomla notably stands out from the other CMS‘s thanks to its quality and usability.
CMS helps to separate design of web site from its content. It means designer develops a web site and gives it to its owner or manager who can fill a certain design with different content. If necessary the content of web site, its images and graphics can be easily edited without intervention into design of web site. All changes become visible as soon as you make them. (Don‘t forget to reload page after making changes). Even if you are not an expert of HTML coding, you can easily manage the content of your web site yourself.