WordPress.org, which is the overseeing organization’s information portal, has a wealth of learning resources available on the site. Many of these are organized into courses with video instruction, text information, practice exercises and quizzes, and the ability to track your progress if you set up an account, which I would recommend. You can find these on the Learn page.
Many of the same videos that are used on the WordPress.org Learn site can also be found on their YouTube page.
WordPress.org ≠ WordPress.com
It is important to know that there is a related WordPress.com page, which is a commercial site that hosts WordPress sites. It is a good option for users who need hosting and WordPress support all in the same location.