The English translation doesn’t quite cut it. Nadi is the channel for energy. Shodana is exploration. Pranayama is taking breath to a different dimension. However, the English translation does indeed portray what we do in the pranayama.
It goes that there are many energy channels inside the body. The three main ones are aligned with the spine. The center one is within the spine (the core of it). The other two are lined up, one on either side of the spine. The left channel is called ida , the right channel is call Pingala.
When a person is balanced, the energy flows equally through the ida and the pingala. However, an imbalance can cause unequal amount of energy flows. So to balance the imbalance, we breathe through both nostrils.
Typically, one of the two nostrils are open. This is nature’s way of bringing balance to the flow. However, to force the balance, you would purposefully breathe (note, not forcefully) through both of them, one at a time.
Sit in a comfortable position. Again, Sukhasana or cross-legged posture is possible with most of the people. If possible get into a half-lotus or even the full lotus posture. In any case, you back should be held up, especially the lower part. The lower part is even tilted a bit to the front. Keep checking the posture over a period of time, again and again.
Press the middle two fingers – index and the middle – into the base of the thumb. Use the thumb to close the right nostril. Inhale through the left. The breathing in Alternate nostril breathing is similar to Ujjayi – complete, continuous, deliberate and producing the Ujjayi sound. When ready to exhale, close the left nostril with your ring finger and open the right. Exhale through the right nostril. Again, inhale through the open right and exhale through the left. That’s it. You practiced one cycle of Alternate nostril breathing. Repeat 8-10 times.
Alternate nostril breathing brings balance to the body. Repeated practice helps you calm down. Make it a habit to practice this pranayama with your yoga sessions.