This page shows an example of an Embed: Content Section (existing section). In this example, the Content Section is being used to display already-created Buttons on this page. This is good for adding reusable content from the Paragraphs library to a page.
You can add a reusable Paragraph (i.e., Content Section, which are called "Paragraphs" by the Drupal module used to create them) via the Paragraphs tab within Content -> Overview.