How to enable auditing in Oracle database

For Oracle versions prior to 9 set audit_trail parameter in ini file i.e.:

audit_trail = DB

For Oracle 9 and later:

alter system set audit_trail = DB;

If you want to audit a specific user run the following:

audit alter table, select table, insert table, update table, delete table, grant table, grant
procedure by USERNAME;

To stop audit for that user run:

noaudit alter table, select table, insert table, update table, delete table, grant table,
grant procedure by USERNAME;

To see the results:

SQL> select * from dba_audit_trail;