How to manage forum permissions in phpBB3
You can change and set permissions in phpBB3 from the the Permissions tab of the administration control panel.
On the left side of the Permissions page there are four sections: Global Permissions, Forum Based Permissions, Permission Roles and Permission Masks. Each section in its turn contains several links.
You can use the links in the Global Permissions section to change and set the permissions for users and user groups (e.g. administrators, moderators, registered users, etc.) for the whole board.
For example, to change the permissions of a particular user for the whole board click on the Users' Permissions link, then type the name of the user in the corresponding field (or use the Find a member link) and click on the Submit button. On the next page you can either select a role with preconfigured permissions from the Role drop-down menu, or you can use the Advanced Permissions button to configure the permissions manually.
The process of changing the permissions for the different user groups is similar; click on the Groups' permissions link and follow the procedure.
To add administrators or global moderators click on the respective link in the Global Permissions section, then find a user you want to add as an administrator or moderator and click on the Add permissions button. Then again you can choose from preconfigured roles or you can set the permissions manually.
From the links in the Forum Based Permissions section you can change and set permissions for specific forums or categories within your board. For example, you can restrict the access to some forums to particular users or a user group that you have created. To do this, click on the Forum permissions link, then select the desired forum/forums (or category) and click on the Submit button. After that choose the users or user groups and configure the permissions. The same can be achieved from the Users' forum permissions or Groups' forum permissions links.
From the Permission Roles section you can change the existing preconfigured roles for each user group, or you can create new roles.
From the last section (Permission Masks) you can view the permissions of the different users, user groups and forums.
For some more details you can also check out the phpBB3 Permissions Tutorial.