If I'm understanding your question correctly... whenever you start a new thread on the forum, or whenever a new reply is posted, "new" will show up for anyone who hasn't yet seen that post. (If you are the one that made the post, though, it won't say "new" -- because you HAVE seen it already) Hope that makes some kind of sense...
And if not, please ask again -- I'm sure someone else will be able to explain it better than I can!