Originally Posted by mzzzquilts

There is a quick reply box right below the opened PM, showing the contents of the PM with the word QUOTE. Click into that. You can either leave all that there and type your reply before or after it, or delete it out. Type your reply, then hit the "submit message" button below the text box. You can also click the "reply to message" button right below the PM and get advanced options instead of the "quick reply".