What does mention do?

The "Mention" allows you to direct a public message to a particular user in the chat room. When you click a user's name and choose "Mention" your message will be visible to everyone in the room. If that user opted in for push notifications, they will receive a push notification, indicating that they have been mentioned. This helps to get the attention of a specific user in a public chat setting.

Please use this sparingly, a better option for ongoing discussions is "whisper". Whisper messages are not seen by anyone but the person you whisper.