You can simply import the jbpm-examples folder in Eclipse to take a look at the processes and test and debug them using the associated Java main classes or junit tests.
The largest set of processes is probably the BPMN2 junit tests. For most of the BPMN2 constructs that are currently supported, there are probably one or a few tests that show how it works. On top of that, there are a few larger examples that show some more advanced features, like:
- human tasks (including user / group assignment, delegation, forms, etc.)
- process + rules integration (see part 2)
Enjoy and learn!