This is an area that you can use to control your home page content that describes your company. You edit it in the custom list named: Who are we? If you change the list title it will change the header of the card where this text is displayed. You can display images and lists and other content available in the editor here.
If you add a URL to this list entry it will show a button where the users can click to read more. It's best to keep this content short and sweet with a url pointing to the page with more content available.