Easier way is at the bottom right of each post are three buttons :
Quote - Press quote on any post to quote that post. If you only want to quote part of the post, just simply delete the line, same as when you're typing normally. Just be sure not to delete the brackets [ ] or anything inside the brackets.
M. Q. (multiquote) - This allows you to quote multiple posts. For every post you want to quote click MQ, when you get to the last post you want to quote click the regular Quote and it will post all the quotes.
Q. R. - This just jumps you to the bottom of the page for a normal Quick Reply.
You can also answer inside a persons quote. Once you've Quoted the post you want to respond to, putting your mouse and clicking where you want to start allows you to type inside the quote box. You can then edit the color/size/font of your response. And can do this multiple times in one quote. This works best on longer posts with lots of points to comment on. Just remember typing inside the quote box does not count as a response to the system, so you will have to type something outside the quote box for it to send.