start srv.py, point your browser at localhost:9000, start playing ;)
(ofc. you need opencv's cv2 module installed. (preferably the 3.0 version)
and, again there are differences between opencv3.0 and opencv2.4.x, if you're using opencv2.4.x, you will have to toggle the comments in blockly.html, line 9/10 )
(no, i did not type all of this, most of it was generated the same way the python api is.)
look at the prj folder for demos.