Comment by:
@ - your character's username - and the comment
e.g.: @VinceyGarrett you're so hot 😉

Like by:
[@ your character's username - like ]
E.g.: [@VinceyGarrett - like]

- updated -
Tag by:
@ -other person's character's username - in the chapter or in comment. (And also tag their wattpad)

DM by:
Private messaging with @ - your character's username - first then the message.