Prana is, according to ancient Indian scriptures, a universal life force that permeates the cosmos and is absorbed through the air we breathe. Pranayama are breathing exercises that calm the nervous system and have a number of benefits. Shortly after these breath work exercises, you'll feel an immediate sense of calm and tranquility. This will be only the first benefit. Other benefits include reduction of anxiety, stabilized blood pressure, muscle relaxation, less stress, and reduced cortisol response in the body.
One of the goals of yoga is to work with the prana and manipulate it in order to revitalize certain parts of your body. For the most skeptical and logical, we can equate prana to the oxygen that gives us life. Using pranayama we can control and manipulate the flow of oxygen (or prana) in the body. Thus, if we use certain asanas (poses) in conjunction with pranayama, we can revitalize and heal our own body. Pranayama is also a great tool for for weight loss.
Usually, when people want to lose weight, the last thing they think about is breath work. Instead, the focus is on cardio exercises, weight training, and diet. But, in addition to the usual benefits originating from a regular Pranayama practice (anxiety reduction, cortisol response lowered, calming down the para-sympathetic nervous system), a new study that just came in the British Medical Journal ties the metabolic process of weight loss to the act of exhaling (Read more here: http://www.iflscience.com/health-and-medicine/where-does-your-fat-go-when-you-lose-weight). As we lose weight, our body transforms most of our mass into carbon dioxide which is then exhaled out making a regular Pranayama practice our best friend in our weight-loss efforts.
The video below presents a basic pranayama practice. It is the same sequence I do every day after my yoga practice. I hope you enjoy and if you have a question, just ask!