Hi,
This is a common scenario, you are jumping from a very simple framework that allows you to create workflows (a little bit more than a state machine) to a full blown BPM tool, which is based on the bpmn2 standard modelling notation (600+ pages of technical spec) so it will denitely not be the same.
You can use jbpm5 or 6 similar to how you used Os workflow but you need to understand the differences first.
I would recommend you to take a look at the examples provides in the book or at the tests inside the framework code base to learn the basics and get you started.
Writing the bpmn2 by hand is usually a very technical task and we usually recommend using the process designe for such task.
Cheers