PL/SQL：Why is SYSDATE and USER keywords used?

SYSDATE: This keyword returns the current time and date on the local database server. The syntax is SYSDATE. In order to extract part of the date, we use the TO_CHAR function on SYSDATE and specify the format we need. Usage:

SELECT SYSDATE FROM dual;
SELECT id, TO_CHAR(SYSDATE, 'yyyy/mm/dd') from InterviewBitEmployeeTable where customer_id < 200;

USER: This keyword returns the user id of the current session. Usage:

SELECT USER FROM dual;