Hello Alexander,
I have implemented a simple web application, which demonstrates how to use jBPM 6 as an embedded engine.
https://github.com/jsvitak/jbpm-6-examples/tree/master/rewards-basic
The second approach how to use jBPM 6 is to leave the runtime inside kie workbench (kie-wb=repo+design tools+runtime+remote api) and control it via remote APIs.
Unfortunately I cannot help you with the docs, as far as I can tell the only source to learn something currently are source codes, unit tests and maybe some blog posts. See also http://planet.jboss.org/post/jbpm_6_0_beta2_available
Jiri