All the users in the 7Cogs organization will be able to add threads (messages) to the forums. If you want them to be able to do more things (create categories, delete messages, etc.) you can use the Control Panel:

1. Log in as Bruno Administrator
2. Go to the Welcome menu
3. Choose Control Panel
4. Click Portal --> Roles --> Define Permissions

All the content in the forums can also be managed from the Control Panel --> Content --> Message Boards

Enjoy!