Ok, all you need to do is ask. When you reply to someones thread, there are 8 buttons below the dialogue box, if you place your cursor at the beginning of the sentence you are trying to quote and push the "quote button" you will see a quote box appear, you then go to the end of the sentence you are quoting and hit the quote button again.
Thus, you have now quoted somebody. I know this stuff can get confusing, if you have any questions feel free to send me a PM (that stands for private message).