Invoke the opath executable and pass it one or more .osm files:
opath scene1.osm [scene2.osm ...]The files are evaluated in order and the environment is kept between them (so symbols defined in scene1.osm are accessible in scene2.osm etc.).
The OSM format (OSM stands for 'OPath Scheme') is a Scheme variant. It isn't a complete implementation by any means although the possibility is there to add functionality as I go along. See chapter 3 for details.
In order to view the images produced by OPath (.hdr radiance compatible by default), you'll need a separate program. Under windows I like to use HDRView: http://www.debevec.org/FiatLux/hdrview/. Under unix systems I've used xview from the radiance package http://radsite.lbl.gov/radiance/. You might also try http://excamera.com/articles/9/vrpic.html, although I haven't tried it.