Everything below the course title is a blank canvas for you to add your description. This is powered by the same WordPress editor used for pages, blog posts and other content types in WordPress.
LearnDash introduces a number of shortcodes & blocks for you to use in this area. You can add a payment button, show or hide content based on a user’s access, insert a course progress bar and more.
For a more detailed look into all of the available options, please read the shortcode & blocks article.