Quoted from website travel.state.gov:
Once you receive your appointment letter, you must register online at www.ustraveldocs.com, select your visa pick-up location, and schedule an appointment for your photograph and fingerprints to be taken at one of our Visa Application Centers in India.
IMPORTANT! Failure to schedule and complete your biometrics appointment at a Visa Application Center will result in the cancellation of your consulate visa interview.