A CMS is a web application you run on your web server to help facilitate creating a website. A good CMS should be flexible, unobtrusive and help you to make a great site. It should provide you with tools to help the layman keep track of content, while letting more experienced webmasters handle look and feel. It should also provide tools to make repetitive things less repetitive. Like, for example, News entries.
I think Wordpress is good, simple, relliable CMS for the freshers.