In this breathing technique, pranayama, the exhale is gently lengthened which helps calm and balance the nervous system, thus calming the entire body and mind. It can help reduce stress and anxiety. The technique is often used in pregnancy and labor, as well.
This is a Yoga Foundations video, aimed at helping introduce you to different yoga poses, breathing techniques, etc. and showing you different variations so you can incorporate them into your personal practice and learn to make them your own.