I'm assuming you're applying in the UK and going to the US Embassy in London, or one of the satellite consulates.
Go to
http://uk.usembassy.gov/cons_new/visa/niv/students.html, read and follow the instructions!
DS-156 is the non-immigration visa application form. You will also need to fill in the Contact Information and Work History form DS-158. Don't forget that you will need your SEVIS receipt for the interview as well.
You'll also need to present a copy of your police record at the interview (
http://uk.usembassy.gov/cons_new/vis...add_crime.html)
For a good overview of whats involved also have a read of BackPackers excellent brief in the Private Flying forum (
http://www.pprune.org/forums/showthread.php?t=278995)