This is an excellent video showing how to practice the “Ujjayi Breath” also known as the “Victorious Breath”, “Ocean Breath” or “Hissing Breath”.
And here is an excellent descriptive procedure of the process: How to Practice Ujjayi Breath in Yoga
Ujjayi is a diaphragmatic breath and so this instructional video may also be of interest:
This technique can be used for pain management, relaxation, and the relief of anxiety. Using this deep breathing technique will help you to rely on your diaphragm rather than your neck muscles, relieving tension, and slowing down your breathing patterns providing relaxation. – Cioffredi & Associates – The Institute for Health & Human Performance