Oracle's own User Guide

1,oracle installation is complete when you create a DB instance, the Sys,system,scott is generated automatically

2,sys user Super Administrator with highest Oracle privileges, SYSDBA role with CREATE DATABASE permission, default password manager

3,system User is the Operation administrator, second only to SYS, with the role of Sysoper (ATE). Syetem does not have the CREATE DATABASE permission, the other permissions are the same as the SYS, the default password is Change_on_install

4,scott User Ordinary user, the default password is Tiger the user is locked by default can be unlocked with the system

PS: General database maintenance, using System User Login

Oracle's own User Guide