The content component (com_content) is what you use to write articles. It is extremely flexible and has the largest number of built in views. Articles can be created and edited from the front end, making content the easiest component to use to create your site content.
This is a module where you might want to add some more information or an image, a link to your social media presence, or whatever makes sense for your site.
You can edit this module in the module manager. Look for the Side Module.
If you are an experienced Joomla! 1.5 user, this Joomla site will seem very familiar. There are new templates and improved user interfaces, but most functionality is the same. The biggest changes are improved access control (ACL) and nested categories. This release of Joomla has strong continuity with Joomla! 1.7 while adding enhancements.