Panels is a combination of composite, node form settings, and several other layout modules on steriods. It's similar to composite in that it allows you to change what content is displayed in the content area and how it is displayed.

Recall the lists below. With the exception of those items noted, Panels allows you to control if, when, and where these items appear on your page. As you make changes to Panels and add modules to your site, the list of items available for you to include in a panel increases.