The main type of breathing we do in yoga is called ujjayi (ooh-JAI-yee). Ujjayi breathing, known as the victory Breath is characterised by an audibly hollow, deep, soft sound coming from your throat.
Ujjayi breathing is not difficult to learn. It involves narrowing the aperture in your throat by gently tightening the epiglottis, which is done like this:
Softly whisper the syllable “ha” with your mouth open. Haaaaaaaaaaaaaa. Stretch it out. Feel the air vibrating softly in the back of your throat. Listen to the clean, hollow sound; it’s similar to the sound of the ocean you can hear in a shell. Produce this sound as if you are inhaling and exhaling. Try it.
Now close your mouth and continue making the same soft, smooth, deep, and hollow sound. This is easiest as you exhale, but it is also possible s you inhale. You are now breathing through your nostrils with your mouth closed, and yet the suction is coming from the back of the throat. The nostrils are relaxed and passive and you will therefore feel the air in your nostrils only very lightly. You are not sniffing the air in. You are gently drawing the air in from the back of your throat. Breathe like this in all the postures.
Source: Erich Schiffmann — The Spirit and Practice of Moving Into Stillness.