First, here is a quick list of some of the RACF utilities and what they do:
IRRMIN00 RACF database initialization utility
IRRUT400 RACF database split/merge/extend utility
IRRDBU00 RACF database unload utility
IRRUT200 RACF database verification utility
IRRUT100 RACF cross-reference utility
IRRRID00 RACF remove ID utility
IRRADU00 RACF SMF data unload utility
To create a new RACF database, you're going to use IRRMIN00. Just whip up some JCL (check out 'z/OS Security Server RACF System Programmer's Guide' if nobody in your shop has some canned JCL you can cut and paste) and the utility will create a fresh database for you to use. Note that you have to reIPL before you can use this new database, as it is completely empty. At IPL time, a user entry for IBMUSER will be added so you can log in and start populating your new database.
After you've done this, there are two commands you probably want to issue against your new database. They are:
The first activates generic profile checking (see this post for a bit more on RACF profiles) and the second activates Enhanced Generic Naming. "When you activate this option, RACF allows you to specify the generic character ** (in addition to the generic characters * and %) when you define data set profile names and entries in the global access checking table. " (Security Server RACF Command Language Reference).