You have 3 different posibilities to enable communication among users and between users and tutors.
If Allow Feedback is checked (course setting) the course participants can send comments to the case authors on each card. These comments will displayed in the authoring system automtically and depending on the authors profile setting also send via email. This feature ca be used e.g. to enable students to indicate errors on the card or ask a question to the author. Reviewer discussion is a variant of this type: Normal feedback can only be seen by the case author, a reviewer discussion allows reviers of this case to see also the messages of collegues and comment on these!
Allow Comments = Tutor triggered comments can be entered by tutors in the reportssection and course manager to provide feedback for the learner. This commenting feature can also be activated in the course manager. Only questions/answers flagges with the corresponding “Allow comments” checkbox in answer options in authoring can be commented by the tutors!
Additionally a course-based “Allow discussion” board can be activated for a course. All course participants can read and leave comments. Also the case authors and course tutors have access to those comments and can reply.
Case rating can be activated and shows up for participants when a case is finished on the case session summary. Social network feature was experimental, the studies didn't show promising results and is deprecated at this point. Will disappear most likely with a next version of CASUS.