After you click the reply button, you will see that at the bottom of the page, there are posts of the other users, you can use the 'Insert quote' option which can be found in the right of each post.
And if you want to quote older posts from previous pages or other threads, you need to click "quote" button on that post, copy that quote and paste it to your post. But if you quoting lot of posts, better to preview it before posting, because it may look messy if accidentally deleted part of "[ quote] [/quote ]"
