This guide is intended to provide an easy way to setting up the opac module for users.
First, you have to download the module itself.
drush dl opac
Enable opac like any other Drupal modules by navigating to:
Admin » modules
Only enable the opac module for the moment which is the main module of the project and let the others (opac items, opac users, ...) disabled.
opac module is for connecting your Integrated Library System (ILS) with drupal. So, you need an ILS working as backend and a connector for this backend.