A content management system (CMS) is software designed to manage content on a Website. Popular Open Source Content Management Systems used today are:
- WordPress - The most popular CMS, and is the easiest to use. You can download a copy from http://wordpress.org/download/ or you can set up a free account at https://en.wordpress.com/signup/ and just play with it to learn how it works.
- Joomla - Is a little more customizable/powerful, but the learning curve is a bit steeper. You can download a copy from http://www.joomla.org/download.html.
- Drupal - Is yet a little more powerful, with a little steeper learning curve. You can download a copy from http://drupal.org/download.
The above three CMSs are probably the most popular ones used today, and they're free to use as open source software. However, you'll need to install it on an Apache Web server running PHP with a MySQL database. If you have a hosting account, the odds are very good that your hosting account will have a ONE CLICK installation icon in the control panel which will allow you to quickly setup and install your CMS.
OpenSourceCMS.com has a demo for hundreds of content management systems at the following link: http://www.opensourcecms.com. This site allows all visitors to act as the administrator of all the different demo CMS installations they list, and it gives you an opportunity to try each of them out before you take the time to download and install. The demo sites automatically reset themselves to the default installation each hour since everyone has administrator access.