Comments can be added to a case when it is being created, when reviewing a case, and even after it has been archived. Open cases can only be commented on when you have ownership of the case; if it was sent to your group, you must take the case before you are able to add a comment. You cannot add a comment to a case that someone else currently has ownership of.
To add a comment to a case:
Step 1: From the Case screen, click on the Add Comment button. A comment field opens at the bottom of the screen.
If the Add Comment button is not visible, make sure that it is a case you are currently working on; if it was sent to a group you are in, make sure that you have taken the case already.
Step 2: Enter text in the Comment field and click on the Save button. The comment is added to the case and will be viewable by those reviewing it.