This is the multiquote button. If you click it, it will light up like this:
. You can click it on as many different posts as you'd like. Then when you click the post reply button
you will get to reply with all of those posts quoted. That is why it is called "multiquote"! Cool eh?
This is the quick reply button. Clicking on it will activate the quick reply button at the bottom. Then if you click the box labeled "Quote message in reply?" right under the entry box, it will automatically quote the message when you post the reply.