Oracle Audit

Hi,
I'd like to Audit log the tasks performed by all users with the exception of 3 schema.
I need to enable the audit on file system in my database oracle 11.2.0.3.0 for 64-bit Windows for all users except for 3 schema (TOM, SAM; SCOTT) , to do this I thought to activate the AUDIT_TRAIL, but I need to know what are the steps.

below the current configuration of my db:

select *
from v$parameter
where name like '%audit%';

NAME: audit_file_dest
VALUE: C:\ORACLE\ADMIN\PR\ADUMP
DISPLAY_VALUE: C:\ORACLE\ADMIN\PR\ADUMP
ISDEFAULT: FALSE
ISSES_MODIFIABLE: FALSE
ISSYS_MODIFIABLE: DEFERRED
ISMODIFIED: FALSE  

NAME: audit_trail
VALUE: DB
DISPLAY_VALUE: DB
ISDEFAULT: FALSE
ISSES_MODIFIABLE: FALSE
ISSYS_MODIFIABLE: FALSE
ISMODIFIED: FALSE

Could someone tell me what are the steps to enable the privilege auditing SELECT, INSERT, UPDATE, DELETE on file?

Thanks in advance!