Oracle: Steps to find session and kill a session

SELECT
vs.username, vs.osuser , vs.sid , serial#, vsql.sql_text
FROM v$session vs , v$sqlarea vsql
WHERE
vs.sql_hash_value = vsql.hash_value
AND vs.sql_address = vsql.address
AND vs.status = 'ACTIVE'
AND vs.username = 'SUBHENDU'


ALTER SYSTEM KILL SESSION 'sid,serial#' IMMEDIATE;