[@Cannon011] I'm personally a little bit confused on the question. :)

So if you're looking to reply to an RP or thread to show interest, you need to click on the link to that thread on the page, then make sure you're in the "OOC" tab (located at the top of the first post on any page of that thread) to say so or post a character sheet.  If you're looking to discuss something in an RP you're a part of in the OOC tab, then yeah, usually we use the "@Mention" or "Quote" buttons to specifically reply to statements/posts from others, so that we don't get lost in the clutter because it will give that person a notification to say that you specifically were looking to reply to them.

If you're posting in the "In-Character" tab, then you shouldn't need to mention or quote the post you're replying to unless that's common custom for that specific group, because everybody is contributing to the same story, so everybody is... essentially replying to everybody.  Again, of course, if the RP in particular mentions the folks involved in the reply to any post on the IC tab, then sure, follow custom.



EDIT: And the "post Reply" button is in reference to the thread on the whole.  It means reply to the thread, so your message pops up last on the page and is added to the discussion/RP.  It's only replying to a specific person if you're mentioning that person.  Otherwise, it's a broad use of the term "reply."