Breathe through both nostrils with the back of the throat gently constricted — as though you were about to fog a mirror, but with the mouth closed. This creates a soft oceanic hiss. The sound is the practice: keep it steady and even on both the inhale and the exhale. Ujjāyī is the one breath used within āsana; it also stands alone as a deep prāṇāyāma when held with kumbhaka.