The demo page and test suite are the best routes to explore the behavior of the processor, in that order. To set up the archive for either, install the processor locales with the following command:
git clone git://github.com/fbennett/locales.git locale
(The official CSL locales live elsewhere,  but you'll want to use this set for processor testing. Note the explicit target directory "locale" [singular] following the repository address.)
To run the test suite, you need to add the standard test fixtures. To do so, enter the directory ./tests/fixtures, and issue the following command:
hg clone http://bitbucket.org/bdarcus/citeproc-test std
(Again, note the explicit target directory, "std", following the repository address.)
For other details, see the manual, either in the ./manual subdirectory under the name citeproc-doc.rst, or online at http://gsl-nagoya-u.net/http/pub/citeproc-doc.html for details of this program.
Hope all goes well. If you have problems, post a note to the issue tracker.