By clicking on the word "quote", the system automatically inserts the BB code to form a box around the post that you want to reference in your own post.
You can also quote multiple people in your own post by simply clicking on the "quote" on all of the posts you wish to reference. You may want to make your own reply in between the quoted areas.
Remember, you can always preview your post and change things if it doesn't look quite right before you post it live.