Plugin for Drupal currently is not open source. Please contact Commercial Support to get it.
You simply download the ZIP or TAR package and unzip it to Drupal "mod" directory.
For a detailed description on how to install plugins in Drupal please review their handbook.
Then you visit the module interface of Drupal, where you will find the new module. You should switch it to "enabled" to get the "Configure" and "Permissions" buttons.
In the configuration you enter the auth data to access your Apache OpenMeetings server:
After installation of the plugin you can go to the front page in Drupal and add a new content item "OpenMeetings Rooms" => "Add New Room". You may find following configuration values for each conference room: