Hi Vincent, what jBPM version are you using? If you are using jBPM5 and are starting off with the jBPM-installer ( http://sourceforge.net/projects/jbpm/files/jBPM%205/jbpm-5.1.0.Final/ ) then please reference the docs: http://docs.jboss.org/jbpm/v5.1/userguide/ch03.html, which should help.
Thanks.