When you create the hello world process, under the project on the left you should see "src/main/java" and "src/main/resources". If you expand "src/main/resources", you can open the BPMN process and add to it, if desired. If you expand "src/main/java" you will get to a Java class named ProcessTest.java. You can inspect this class to see how it is running the BPMN process. You can right-click this Java class and click Run As > JUnit Test. You should see it output "Hello World" to the console.
For a tutorial on how to use jBPM in Eclipse, there is a short tutorial video in the documentation: http://docs.jboss.org/jbpm/v6.0.1/userguide/jBPMInstaller.html#d0e780