The synchronization is "one-way" - from Organic Groups to CiviCRM Groups.
Once the module is enabled via Drupal Administer » Modules - for any new or re-saved Organic Group it will automatically create 2 CiviCRM groups:
NB: there are no configuration settings in Drupal - so don't stress if you can't find them!
When a new user is added / signs up for an Organic Group, they are automatically added to the corresponding CiviCRM Group.
NB: for existing OGs the synching only seems to only add the Manager in to the Civi 'Admin' Group, not the other Admins. Removing and recreating their OG Admin-ness sorts it..
Reverse Synching ie CiviCRM > OG
For some discussions about reverse synching try these forum posts
Importing CiviCRM Contacts to OG
A useful tool for grabbing CiviCRM contacts to add to the OG (if you don't go down the 'reverse synch' route) is User Import Organic Groups - http://drupal.org/project/user_import_og
Just export CiviCRM contacts' emails and add Drupal users to the OG, or create them on the fly (in which case also export First Last to build the user name from).