You have two options, one is to use Designer to generate your process and task forms for you, for that click on the:
https://community.jboss.org/servlet/JiveServlet/downloadImage/2-778892-19944/17-19/button-create-task-forms.png
in the navbar. You can then edit your process and task forms in Designer as well, for that see: http://surdilovic.wordpress.com/2012/08/06/process-and-task-form-editing-in-jbpm-designer/
HTH
