Matt Mullenweg released WordPress in 2003 as an open source software. WordPress now powers over 200 million websites worldwide and is maintained through an open source community. WordPress.com offers a hosted version of WordPress that is easy to use but limited, while WordPress.org allows for more customization through plugins and themes but requires installing and maintaining the software. The document then provides instructions on installing WordPress and an overview of common features like pages, posts, categories, themes, widgets, and plugins.