Internal Msg enable user to send internal messages directly to one or many of other users. Internet connection is not necessary when using Internal Msg.
Click on New Message to write a new message.
Click on Check New Messages to check for newly arrived messages.
You can add new message box via Message Box Settings. Click on Message Box Settings, then click on Add to add a new message box. You can save messages in specified message box, or move messages from one box to another.