1. Look at the lower right corner of a post.
2. You'll see a button that says "quote"
3. Click on it
4. write reply
5. post reply
6. done.
7. ???
8. PROFIT!
A. Alternatively, you can use the [QUOTE] tag.
B. There's also the "multi" button which allows you to select several posts at the same time. When you click quote, they will all be quoted. Try it. Click on several "multi" buttons. They will be highlighted. Then click on quote.
Fixed it for ya!

No, it may look like you're starting a new thread, but if you look at the bread crumbs at the top of the page you'll see it says 'Reply to thread' and not 'create new thread'.