What are the DS forms?
While booking the date online, you need to fill in three DS forms, i.e. DS-156, DS-157 and DS-158. Find samples of these forms at http://www.immihelp.com/visas/student/f1-visa-documents.html You will have to take a printout of these filled forms with you for you Interview. You can edit these forms even after booking your date except for details like Passport Number, Place of Issue, Date of Birth etc.