The breath of fire or the skull shining breath is invigorating, energising, and purifying.

Kapalabhati is a very active, forced exhalation with a passive inhalation. To exhale, the belly quickly pumps into the spine forcing the air out of the nose (like trying to blow out a candle through your nose). Place a hand on your belly to feel the belly actively pumping. Play with the tempo (45-60 exhalations/30 seconds), but keep a steady rhythm. Start with 2-3 rounds of 30 exhalations, and gradually increase the exhalations if comfortable. 

Practice this seated in Baddha Konasana ( Bound Angle pose or Butterfly Pose ) with the arms behind you fingers pointing forward, to allow the chest to open and gain maximum space for the breath.