For those very new to the forum who do not know how to 'quote' a previous post:
When you want to reply to a particular post you click on the 'quote button' that looks like this - it is located in the right-hand corner of someone's post.
By clicking on the 'quote' it will bring up a reply box but it will have already in it writing from the other person.
Click after the last line where it says [/quote]
Put 2 spaces and then type what you want to type and hit 'submit' as you normally would.