Please explain SYSCS_UTIL.SYSCS_CREATE_USER() function

Can someone please explain to me how SYSCS_UTIL.SYSCS_CREATE_USER() works? I tried adding a new user like this: SYSCS_UTIL.SYSCS_CREATE_USER('user', 'someP@ss'), and it gave an exception *Error code 30000, SQL state 4251K: The first credentials created must be those of the DBO.* I found the function in the Derby Docs, but it showed the Fred example, which I also tried, but it gave me the same exception. I created the database via NetBeans.