[Forum] How to set user group permissions?

[DejanK]

I'm having an issue setting permissions.
I created a separate forum and I want users to have 1 post before being able to post in this section.
How can I do this?
I don't want to limit all registered users so I tried creating a user title but then I can't go about setting permissions for user titles.
I tried doing the Promotions for user groups but each time it tells me invalid user group selected.