If you just want to quote this one post (like I did with yours), you need to hit the Reply button. This will insert the quote into the reply box on the bottom of the page. If you want to reply without a quote, you just start typing in the reply box.
Btw, you can even hit the reply button on multiple posts and they all will be added to the reply box (another way of multi quoting). But it only works on the page you are currently on.