In forum management make a new forum.
Then make another forum.
Parent: the category you just made.
Then you need to set permissions so everyone can see it:
Admin control panel>Permissions>Groups forum permissions.
Set the registered users to be able to see and post in it:
Registered users>Standard access
If that doesn't help, :
Please fill out the Support Request Template Generator
and post it back here to enable us to assist you better.