To perform chin mudra the tip of the first finger is placed at the root of the thumb and the palms are turned upwards with the back of the hands resting on the knees. Turning the palms upwards also has a broadening effect across the front of the shoulders which in turn allows more space for our breathing and heart function and subtly lifts our spirits.
Alternatively the thumb can be placed at the tip of the first finger.

The thumb is analagous to the Supreme Soul whereas the first finger is analagous to the individual soul or self. Therefore in chin mudra we are performing Iswara Pranidhana - the offering of reverence and respect to Iswara (the Supreme Soul).
Iswara Pranidhana is one of the Five Yamas or codes of conduct for living as taught by Patanjali in his treatise The Yoga Sutras. If you are interested in learning more about the yamas or the teachings of yoga I often mention them in our Yoga Mini Retreats at Fradgley Hall on the third Sunday of the month.