ok I have read this

Only registered users can see links on this forum! Register or Login on forum!

but it really didn't tell me what I wanted to know.
it said I CAN make the whole forum private but HOW do I do that?

Thanks!

Read through the whole guide. It explains everything you need to know.

You have to set the permissions to "private" for each section on your forum. There is not a way to make the whole forum private with one click.

Also, as the FAQ says, you then have to make a private group, set the permissions for that group to be able to view, read and post, and put your members in it. If you don't, they won't be able to see anything on your forum.