XF 1.5 How to set one forum as support desk

I have a forum that I want to use that as support desk.

How to set it so that:
1. User 1, user 2 ,... can post a thread, but they only can see their thread , not others.
2. User 1, user 2,... can see admin's threads.

I can set permission for 1. How to set 2.