How to add a "sign up" field with theClassifieds plugin

How do I add a sign up field for the following:
http://www.swipswaploxahatchee.com/classifieds/signin/?redirect_to=http%3A%2F%2Fwww.swipswaploxahatchee.com%2Fclassifieds%2Fmy-classifieds%2F

Thanks!