For issues related to finances, the best sites to visit are the following:

Office of Scholarships and Financial Aid - This office identifies students for monetary assistance through financial aid or through scholarship awards. If your student has not filled out the Federal Application for Financial Aid (FAFSA), please do so. This is required for University aid consideration. http://www.okstate.edu/finaid/

Office of the Bursar - http://bursar.okstate.edu/-
This office is the primary billing entity for student accounts. Typical billing items include tuition/fees, room/board, books, athletic tickets, and parking permits.
The Bursar's website includes a Parent and Student Guide outlining basic information. Visit http://bursar.okstate.edu/forms/osupop.pdf for Payment Option Plan application and http://bursar.okstate.edu/forms/ddrevision.pdf for the direct deposit form.