Hi there, you can take a look at my personal blog. I have a couple of post about that. I've also published a book about jBPM3, and I'm currently working in a new version for jBPM5.
JBPM provides you with "workflow" support. Every time there are multiple people/applications working on a shared ressource, there is place for "workflow".
For instance in a retail B2C activity. You migth have single orders comming from customer through a front office. Theses orders concerns probably in the end multiple things to put into action through a backoffice (packaging, tracking, invoice and shipment). Some of those things (physical or not) are shared between multiple customers. Here is where BPMN is supposed to help you.
A BPMN diagram is a way to describe human and applications processes as successive states (wait states and activities) where one and only one actor plays its independent role.
Now JBPM the java implementation of that does not provides you with anything else than
- a database for storing processes deployment and executions persistence,
- process langage engine for both native JPDL and BPMN2
- graphical editor for JBPM and BPMN2 either for Web (Signavio) and Eclipse (GPD and a great plugin form Koen, see discussions)
- basic people and group support
- task assignement and mail notification mechanisms
- process variables
- History support
It's up to you to provide Web or heavy client integration. You migh use any kind of MVC solution as well as transaction coupling techniques between your database dans JBPM database.
The aim in this BPMN "new" approach is : how could we let managers simply design graphical workflow and let technicals deal with every following "applications details". Actually this question holds from the 70' if you remember what was SA/SADT/IDEF0 and many other formal things from that time.
You migth read out how Tom Bayens describes the basic paradigm: a good software application is always waiting for human and/or others applications. Therefore in 99% of cases, the workflow actually takes place in a single thread. The same holds in the real time field with other kind of technologies doing very comparable things indeed.