Everything about concrete5 is completely customizable through the CMS. This is a separate area from the main content on the homepage. You can drag and drop blocks like this around your layout.
Content Management is easy with concrete5's in-context editing. Just login and you can add and change things as you browse your site.
Here's some videos you can watch learn how to:
We've taken the liberty to build out the rest of this site with some sample content that will help you learn concrete5. Wander around a bit, or just goto the Dashboard > Sitemap and delete the parts you don't want quickly.