Alternate. Nostril. Breathing. As in, you cover one nostril to inhale, cover the other nostril to exhale, and then reverse it. The article suggests starting with 12 repetitions and building up, which leaves one with the vague impression that you will be otherwise overwhelmed by the intensity of the experience. (Admittedly deliberate breathing exercises can carry the risk of hyperventilation, so maybe that’s all they meant. But they don’t say so.)
Apparently it improves brain function, regulates your body temperature, and clears stale air from your lungs. Of course it does.