Hello balajiyes,
I think I have cleared mentioned spool 'file name'

let's say you spooling output into a spool file and you wana datestamp before the file name like below example.

column col1 new_value myfile noprint
select to_char(sysdate,'YYYYMMDD') col1 from dual;
spool c:\&myfile.txt OR spool c:\&&myfile.txt
.
.
spool off

Now the question is what is the difference between & and && in sql*plus spool file, see below
spool c:\&myfile.txt;
and
spool c:\&&myfile.txt;

Thanks in advance.