In this chapter Karen Stevenson explains all the pieces that make up an Organic Group content type. Show explains how organic groups adds the necessary fields to make this happen while demonstrating the necessary settings when building your content types. She also covers the content type used for group content as it is different than the group itself. To start the video off she goes over install the necessary modules for the first part of this series.
Note: There have been significant changes to Organic Groups since this lesson was made. Though we would like to revisit this series to update it, we have no current schedule to complete that. The best place to figure out what has changed and why, would be the Organic Groups issue queue on Drupal.org (http://drupal.org/project/issues/search/og).