WordPress is free and open source tool and content management system (CMS). It is based on PHP and MySQL.It runs on a web hosting service. Features include plug-in and a template system. WordPress is used more than 18.9% of top 10 million websites. WordPress is the most popular blogging system in Web and used in more than 60 million websites.
WordPress users may install themes. Themes allow users to change the look and functionality of a WordPress .Install the themes with there content. Themes are installed using the WordPress “Appearance” administration tool or uploaded on theme folder via FTP. The PHP, HTML & CSS code found in themes can be added or edited for providing advanced features. Thousands of WordPress themes are there and some are free and some are premium (paid for) templates.
The downloading link of wordpress is : http://wordpress.org/download/