You can see jBPM5 as a set of APIs that let you execute BPMN2 diagrams. In fact, using the framework is relatively easy:
- ksession.startProcess();
- ksession.signalEvent();
- ksessiong.getWorkItemManager().completeWorkItem()
- Human Task client APIS to complete, delegate, escalate Human Tasks
There are a few more methods, but these are the most important.
So, who is in charge of execute these methods is up to your own application. You have to code the way users interact with the framework.
There is a 'canned' solution called jBPM-Console that serves as a runtime environment for your processes. If the features provided by this application are enough for you (I'm 80% they are not :) ) you can use it. Otherwise, you will need to code your own application what will be in charge of create a kbase, add all the assets to the kbase, create a ksession when it corresponds, initiate th processes when needed, etc.
Of course, jBPM-Console is open source, so you can use it as a base to your own implementation.