After you hit repy, if you look at the post to which you are replying, in the upper right corner of it you will see "insert quote." If you click on that, the entire post will be added to your reply as quoted text. Like this:
How do I copy and paste a quote in a response 
E X
When you do this you will notice that at the beginning it says [quote and a bunch code stuff] and at the end of the quote text it says [/quote]. If you don't want to be quoting the entire post, you can delete that parts you don't want, just be sure that you keep those brackets in place.
You can also copy and paste just the portions of the post that you would like to quote. Then high light it and click on the button that looks like a cartoon character speech bubble (in between the # button and list above the color spectrum thingy).
It will look like this if quoted this way:
How do I copy and paste a quote
HTH
