Add the URL of the page you want to link to and clickon "Fill page details". The details and image of the page will be retrieved and filled in automatically. Edit any fields if necessary. After you are finished, click on the “Publish” toggle and save the content.
Note that Drupal is not always able to fetch the image and information automatically, or they may not work for your content (this depends on the content you're linking to). If the details and image are not fetched automatically or they do not work for your needs, add an image manually and add or edit the text.