To send a private message to a user, double click on his/her name or image in the "Users list" then a popup window will open. You can send and receive private messages in the window. When a user sends a private message to you for the first time, this message places in this list with a different color (usually yellow). If you want to have a private session with sender of message, you can click on this message.

Just double click on your desired room in "rooms list".

IMPORTANT NOTICE : It takes a time to leave a room and enter another room so don't double click more than ONE TIME.