I've been told by HC Support that I can tag messages to specific...

I've been told by HC Support that I can tag messages to specific users and they get a message telling them that they've been "tagged" (???).  After that you can start your own private thread or something along those lines anyway.  In any case I don't know what it means, nor can I find any information re tagging, or how you do it, etc.  I would like to talk about the outcome of my discussions with the Takeovers Panel with those who expressed their interest in possibly doing something about this rights offer.  If any of you know what tagging means and how to do it please "tag" me and hopefully the rest of whatever happens after that will become clearer.