You can tag a user who is together with you in the group chat room. After doing this the name of the user will appear as a hyperlink in your comment leading to the user's profile. To mention a user you need to do the following:
1.Start typing "@" character
Mention a user
2.After this the list of all users added to the chat room will appear. You can either select a user from it or continue typing user's name after "@" character
3.Send a message with @mention
@mention feature helps to collaborate more effectively, ask a question or discuss something.