Steps to enable the Archivelog mode

ALTER SYSTEM SET log_archive_start=TRUE SCOPE=spfile;
ALTER SYSTEM SET log_archive_dest_1='location=/u01/oradata/MYSID/archive/' SCOPE=spfile;
ALTER SYSTEM SET log_archive_format='arch_%t_%s.arc' SCOPE=spfile;
SHUTDOWN IMMEDIATE;
STARTUP MOUNT;
ARCHIVE LOG START;
ALTER DATABASE ARCHIVELOG;
ALTER DATABASE OPEN;
alter system switch logfile;