How to add new categories and forums in phpBB3
In phpBB3 you can create separate categories, each of which can contain many forums. Each forum in its turn can have many subforums and topics in it.
When you make a new installation, by default there is one example category (Your first category) with one forum in it (Your first forum). You can add new categories and forums from the administration panel of your phpBB3.
After you log in to the admin panel, click on the Manage forums link on the left side of the General tab page, or click on the Forums tab. Then type the desired category or forum name in the text field in the lower right corner and click on the Create new forum button.
A new page with different options will open. If you want to create a category, set the Forum type drop-down menu to Category. You should also set the drop-down menu Copy permissions from to Your first category, the default example category. In this way the appropriate permissions from the preconfigured default category will be copied to your new category. Otherwise, you have to configure the permissions manually.
Optionally, you can configure the rest of the settings, or you can directly click on the Submit button at the bottom of the page and the category will be created.
To add a new forum, after you click on the Create new forum button, set the Forum type drop-down menu to Forum. From the Parent forum drop-down menu select the category in which you want to put the new forum, and from the drop-down menu Copy permissions from select Your first forum. After that you can click on the Submit button.
After you create your first new category and forum you can either delete or rename the default example ones.
You can also check out the tutorial on adding categories and forums in phpBB3.