Create a user.
  
  Syntax:
   CREATE USER username
      IDENTIFIED {BY password | EXTERNALLY | GLOBALLY AS 'external_name'}
         options;
options:
   
   DEFAULT TABLESPACE tablespace
   TEMPORARY TABLESPACE tablespace
   QUOTA int {K | M} ON tablespace
   QUOTA UNLIMITED ON tablespace
   PROFILE profile_name
   PASSWORD EXPIRE
   ACCOUNT {LOCK|UNLOCK}
EXAMPLES
-- Create a user with no rights to save data or create objects:
CREATE USER limited IDENTIFIED BY ChangeThis;
-- Create a user with full rights to create objects and save data:
DROP USER MySchemaOwner CASCADE;
CREATE USER MySchemaOwner IDENTIFIED BY ChangeThis
       DEFAULT TABLESPACE data  
       TEMPORARY TABLESPACE temp
       QUOTA UNLIMITED ON data;
CREATE ROLE conn;
GRANT CREATE session, CREATE table, CREATE view, 
      CREATE procedure,CREATE synonym,
      ALTER table, ALTER view, ALTER procedure,ALTER synonym,
      DROP table, DROP view, DROP procedure,DROP synonym,
      TO conn;
GRANT conn TO MySchemaOwner;
You have to create a user first before you can GRANT permissions, roles or assign a default ROLE.
"If you bungle raising your children, I don't think whatever else you do well matters very much" ~ Jacqueline Kennedy Onassis
Related Oracle Commands:
ALTER USER DEFAULT ROLE 
DROP USER
GRANT 
Related Views:
                                           USER_PASSWORD_LIMITS  
                                                                SESSION_ROLES
                                                                SESSION_PRIVS
                                                                SESSION_CONTEXT
 DBA_TS_QUOTAS                             USER_TS_QUOTAS
 DBA_USERS            ALL_USERS            USER_USERS
 V$SESSION
 V$SESSION_CONNECT_INFO