or, if you mean 'start a new forum', you have to start with a Member Social Group. then once you have 20 (i think) members, you can take it public as a Social Forum (listed at the very bottom of the Forum Index).

go to..... (here) http://forums.psychcentral.com/group.php?do=create
(i used my profile page, member groups link), and just fill in the blanks. then you might let people know, in other Forums that the people you want to communicate with might be in, that there is a new social group.

you can make your group Private, Invite Only, or Public. each of these changes who can read the posts and who can join, and how.

if you want more help with this topic, feel free to drop me a note, or a PM.
best wishes~