In the tab for "Activities" different actions can be created that will affect the selected Internal activity. Depending on what that action is, it will change the status for the affected Internal activity. As of right now that status can be "OK", "Exception", "Suspended", and "Created".
Different mails will be sent to different users depending on what status the Internal activity has. To create/edit messages the tab "Output" is used. To make it easier to find the information each tab will have its separate documentation. See the links below.