Creating a multi-person chat
Click on "Start Chat" and select the users you'd like included in the chat. Selected users show up in blue and they need not be online to be added to a chat. Note that you, the logged in user, will never show up in this list: you're always a member of any chat you start.
You can add new users to the char once it's started by clicking "add more" in the chart's right hand "Members" tab. Only users who are listed in the Members tab of a chat can see the chat: it will show up in their "My Chats" tab and they'll receive notifications of chat activity if they have that set up.