To quote just some of the text (using a Windows computer)

1. Select (highlight) the text you wish to quote.
2. Press Ctrl+C to copy to your clipboard.
3. Click the Reply button.
4. Press Ctrl+V in the Full Reply window to paste the text you just copied.
5. Select that text, and click the " (quote) button.

[quote]PS How do you get the quotes to appear in a box?[/quote]

Someone else will have to do the Mac instructions.
While you are in the Reply screen, you can change fonts and colors. The Quick Reply box does not include the formatting buttons, although you can add the formatting codes directly (if you are of the geek persuasion).