The message section allows you to PM (private message) other users and uses the standard posting interface.
If you have any unread messages, you will be notified on the home page with a link directly to the message in the personal section.
You also have your unique profile. This allows you to create a signature that will append any forum post. It also allows you to customise how you view the site, changing the colour template.
This allows you to decide what you want showing on the home page. There might be forums or sections that have no interest to you and as such you have the capability of turning off home page notification.
This lists all the groups you belong to and your rights within the group. Below your access status are links and recruitment paths to joining other groups.