Well, you first have to have 10 posts here on DISboards. You currently show 9 posts.
Once you've done your 10th post, it does take the system a bit of time to recognize it (30-60 minutes). Once it does, you can start a conversation by either clicking on someone's avatar and using the "Start a conversation" link. Or hovering over the "Inbox" link in the upper right and clicking on the "Start a New Conversation" link in the pull down.