Managing Drupal Forum Permissions
Registered users can comment on Drupal forum topics. However, default permissions make it so you’re the only one who can post forum topics. Because the point of having a forum is to elicit discussion from visitors to your site, you will want to allow other people to post forum topics. This is controlled by the permissions settings for the Forum module.
Using the Dashboard menu bar, select People and then click the Permissions tab. When the Permissions overlay opens, you see a number of permission options related to how users interact with your site’s forums. The forum permission topics are
Administer Forums: Grants permission to create, edit, and delete containers and forums.
Forum Topic: Create New Content: User is permitted to create new forum topic.
Forum Topic: Edit Own Content: User can edit only forum topics she has created.
Forum Topic: Edit Any Content: User can edit all forum topics, not just his own.
Forum Topic: Delete Own Content: User can delete only forum topics she created.
Forum Topic: Delete Any Content: Grants permission to delete all forum topics, not just ones created by this user.
If you trust your authenticated users not to abuse the privilege, allow them to create new forum topics, delete their own forum topics, and edit their own forum topics. Doing so makes for a much more vibrant online community that will keep your users coming back for more, time and time again.