Silly forum semi-technical question - reply to use tagging

[Michael Wolffs]

I've been here for a while, and there's something I've never figured out about the forum interface.  

I see replies starting tagged with the @<username of user being replied to>.  But I see no "reply" button or anything of the sort.  I think I tried starting my posts typeing "@<username>" but it just came in as plain text.  

I'm clearly missing something, but I don't know what it is.  I'm usually good with technical issues, but I'm not getting this one.