The history of WordPress started out because the development of an existing blogging software b2/cafelog was discontinued by the main developers. In 2003, Matt Mullenweg and Mike Little decided to build a new platform. On May 27, 2003, Matt Mullenweg announced the first version of Wordress v1.0 and it was well receieved. In 2004, plug-ins were introduced to WordPress v1.2 and users had the ability to create their own plug-ins and share them with the community. In 2005, WordPress v1.5 introduced pages, comment moderation tools, and a new theme system. Towards the end of the year, WordPress v2.0 was released with a new admin dashboard. March 2006, Matt Mullenweg filed the trademark registration for WordPress and the WordPress logo. By 2008, a web design company called Happy Cog joined the WordPress project to help design a new WordPress admin interface. Eventually by 2010, Matt Mullenweg transferred the ownership of WordPress trademark and logo to the WordPress Foundation to ensure WordPress will continue to grow and not be dependent on a group of developers. As years went on, more and more features were introduced such as taxonomies, custom posts, custom backgrounds, headers, and menus. To this day, WordPress is still evolving and adding more features for users.
WordPress.org is a self-service where you can download the software itself and use to build and maintain a website on your own.
WordPress.com is a service that helps you build a website using the WordPress software with managed hosting.
In summary, WordPress.com and WordPress.org are two different platforms, but also two useful services that allow you to create and manage your website. They both have plenty of resouces to help you learn how to manage your content on the web.