RTRR, when you reply to a post, there should be a little "quote" box located in the left-hand column of the "add reply" page.
It will be listed about half-way down under Comment.

Comment:
Insert:
"image"
"link"
"email"
"quote"
"center"
"code"
"hr"

It makes posts a lot easier to read for people when you put text that you're quoting in a quote box.