In the upper right had corner of the post you will see a quote button. Hitting that will start a reply with the text from that post. If the quote is excessively large, you can trim it down then make your post under the remaining text. Use the preview button on the bottom to see what it looks like before you hit the post button. The [quote][/quote] marks the text as a quote so you don't want to tamper with them and it's best to place your comments outside them.
Other format items can be found
here and on the post page you will find automatic insert codes above the text box. Just highlight the text and hit the desired icon.