You may use CMS WordPress to build a website.
WordPress is free, easy to use and the most popular CMS.
You have 2 ways to build website with WordPress:
- WordPress.com - like rented flat, much work made for you
- WordPress.org - like own house, you do all the configuration, but you get more freedom
Difference between wp.org and wp.com is that wp.com is hosted WordPress service (and all the work is made for you) and wp.org is a self-hosted and you should do all the hosting and site configuration.