Oracle has predefined accounts which are SYS and SYSTEM user. These users can not be drop. SYS user has all privileges with Admin Option. If you want to connect SYS account, you must use the AS SYSDBA or AS SYSOPER clause. Any user can connect SYSDBA privilege by using the AS SYSDBA clause. Only privileged users who are granted the SYSDBA or SYSOPER privilege are allowed to STARTUP and SHUTDOWN the database instance.
Create and Drop User
CREATE USER User_Name IDENTIFIED BY User_PassWord;
DROP USER User_Name;
Create and Drop Role
CREATE ROLE Role_Name;
DROP ROLE Role_Name;
Grant and Revoke
GRANT create table,create sequence,create session,create procedure,create view to User_Name (User,Role,Public) [WITH GRANT OPTION]
Note : If you use WITH GRANT OPTION, This user can give own role to other user.
GRANT update(department_id,department_name) ON departments TO Role_Name;
REVOKE create table FROM User_Name;