Hi Shameen,
Download the form from
http://cbse.nic.in/faq/dupform.pdf .
Fill it up amd don't forget to mention the amount you made a DD for.
Make a demand draft from any bank.The amount to be paid depends on how old the marksheet is.The DD should be made in favor of secretary cbse and mention the Regional office.
Mail the form and the DD photocopy to your regional CBSE office,as mentioned in the last page of your application form.
Thanks!