I would recommend trying the installer: it will install a lot of tools and show you a working example. After that, you can start playing with it, change the example, create your own example, etc.
https://hudson.jboss.org/hudson/job/jBPM5/lastSuccessfulBuild/artifact/target/jbpm-5.0-SNAPSHOT-docs-build/jbpm-docs/html/ch02.html
Kris