Messages allows you to send and receive private messages to site participants or groups within your site. Users will be notified if they have any unread messages in their Message Center Notifications in Home.
To see if someone has added a new message or forum posting to one of your sites, go to Overview in Home. Under Messages Center Notifications, you'll find a list of your sites, and the number of new messages and forum postings for each. If there are no new messages or forum postings, you'll see None beside your site.