How do I add Internal Comments on a Case?

In Cases, you can add a comment and mention other users. 
 For example, as a team manager, you might need to interact with a support rep while reviewing a case. Or, as a support rep, you might sometimes want to reach out a colleague to get clarity on a case.
 In such situations, you can mention your team manager or colleague on a case. To do this, click the Comment button under the Activity section in the case’s Summary View.
 When you mention a user, they will be notified under Main Menu > Essentials > Actions.