The best introduction is probably Integrate You Logistic Processes with OpenERP, a free ebook written by OpenERP S.A. themselves[1]. It's slightly outdated, since it was published in 2011 and meanwhile version 7.0 has been released, but the changes to the stock area where limited (except for the UI).

We have a demo instance for version 7.0 [2], but it's in Portuguese (though you can change the language). OpenERP S.A. offers a free trial.

[1] http://www.brain-tec.ch/ebusiness-de-2/openERP/logistic-proz...

[2] https://demo7.thinkopensolutions.com/?db=demo&user=demo&pass...