Shut the database

Backup the database

Modify/Include LOG_ARCHIVE_START_TRUE in init.ora file.

Start up the database.

To enable archiving

first shutdown the database in normal mode

then open ur parameter file and include a parameter

archive_log_dest=(give a OS level location)

then come out of it and at OS level create same directory which u have just mentioned in parameter file

then startup mount

then alter database archivelog

then alter database open

in order to know whether ur database is functioning in archive mode or not

type at sql promt

ARCHIVE LOGLIST;