Answer 1

SYS
Automatically created when Oracle database is installed
Automatically granted the DBA role
Has a default password: CHANGE_ON_INSTALL (make sure you change it)
Owns the base tables and views for the database data dictionary
The default schema when you connect as SYSDBA
Tables in the SYS schema are manipulated only by the database. They should never be modified by any user or database administrator, and no one should create any tables in the schema of user SYS. Database users should not connect to the Oracle database using the SYS account.
SYSTEM
Automatically created when Oracle database is installed
Automatically granted the DBA role
Has a default password: MANAGER (make sure you change it)
Used to create additional tables and views that display administrative information
Used to create internal tables and views used by various Oracle database options and tools
Never use the SYSTEM schema to store tables of interest to non-administrative users.