I've never been entirely certain how it works even though I keep getting credit for doing it. I think it relates to "tag" words or phrases in a particular thread that if mentioned in a new post to refer back, as it were. You'll see "tag" phrases listed at the bottom of threads. I've given up trying to work out how the ranking scoring works though.
No mate, it's just a way of contacting another member directly saving the bother of trying to wait for him to be back online then hijacking a thread. It gives a pop up notification to let them know they've got a message. It's just for stuff that doesn't need to be private.