Forum privacy setting?

Newbie question - I'm missing something here. How does the privacy setting for individual forums work? I don't get how you assign specific users or a user group to a private forum. If I choose that setting, I'm the only one who can access it, as the site owner. What am I missing?

Oh - I guess I do need to have a membership level that has private forum viewing and whatnot enabled? So I can't create permissions specific to any given forum? ...it would have to be a group I suppose - not really what I was hoping to do.