Drupal is many things. It is an open source project like Firefox project. Unlike Firefox which is managed by the Mozilla Foundation, Drupal is managed by the Drupal community. Drupal is also a website. Drupal.org is where most code that makes Drupal sites work including the core Drupal project. All Drupal websites run a version of core. What makes each website different are the additional contributed modules that are added. That is often referred to as Contrib. These contib modules do everything from allow Drupal to understand and manage Dates to display Video.

The Community Media Starter Kits combine Drupal core + Contrib modules + modules written specifically for Community Media.

It is important to have a basic understanding of which modules are providing what functionality to find the documentation and get support. While the Community Media Starter Kits include all of the modules you'd need to create a website, there are thousands of modules that can add additional functionality to your website that you may consider adding.