You can use BBcode! Take whatever you want to quote, and put it in brackets (NOT PARENTHESES--I'm only using them so that it doesn't actually code things).
(quote)text(/quote)
It should look like:
text
Graffiti is the most passionate form of literature there is.
There's also a quote button in the list of buttons above the message box. Go past the bold, italic, and underline buttons to find it.
You can hit the quote button first, enter the text you want, and then click the 'Close Tags' link after the fonts. Or, you can enter the text you want, highlight that, and then hit the quote button. Either will do.
Another method is hitting the 'quote' button at the top of some one's post in order to reply. That will give you the whole post in quotes.
Some people fall in love and touch the sky.
Some people fall in love and find Quicksand.
