Adi mudra is considered the first mudra because it is the first position an infant can make with the hands. It is often used while practicing meditation, and is thought to aid in pranayama because it increases breathing and lung capacity, thus increasing oxygen flow throughout the body.
The adi mudra is also thought to stimulate the brain, which is closely related to the crown (sahasrara) chakra that governs an individual's sense of peace, higher awareness and oneness with the universe.
It is recommended to practice adi mudra in a quiet setting while meditating and focusing on the breath, with the palms facing down on the thighs in a seated pose, such as padmasana (lotus pose). Because this mudra calms and soothes the nervous system, it can be beneficial to incorporate into the end of an asana practice.