Second level primary links block

On this site you will notice that clicking the primary links located in the black bar above will update a block on the left presenting the second level (and below) of the primary links. This is common, but not so straightforward in Drupal. Download and install the submenu tree module. This module is intended mainly to fill parent menu items with a list of child menu items automatically. As a bonus you will also get the Extended primary links block. This is what we need. Just enable this block and you are done.