Prana means life force or vital energy. Ayama is the opposite of yama. Ayama is extention or lengthening, as Yama means restraint or restriction. Pranayama is often translated as breathing exercises while what it really refers to is both the expansion and control of prana. Initially one is introduced to pranayama through "breathing practices" in yoga class which we discover have a remarkable calming effect on the mind. Why is this? We are concentrating our minds, and therefore our energy, on the breath. Slowing down our busy minds relaxes us and allows us to focus our energy better without getting scattered. My teacher has a habit of repeating, "where the breath goes, prana follows". In other words, bring your attention to your breath and get your energy under control!
There are a great many pranayama practices, each one more sophisticated than the previous, designed to take our minds and our energy to an ever increasing state of refinement. "What we want to do is to feel the finer motions that are going on in the body. Our minds have become externalized and have lost sight of the fine motions inside. If we can begin to feel them we can also begin to control them". That is how Swami Vivekananda exlains what we are trying to do with pranayama in Raja Yoga. It is how he summarized the more complex explanation he gives on psychic prana, explaining the ida and pingala currents which carry prana from the base of our spines up to the brain. "according to the Yogis, there are two nerve currents in the spinal column called the Pingala and the Ida, and a hollow canal called the Sushumna, running through the spinal cord. At the lower end of the spinal cord is what the Yogis called the lotus of the Kudalini. When the Kundalini awakes, it tries to force a passage through this hollow canal;and as it tries step by step, layer after layer of the mind opens up and many different visions and wonderful powers come to the Yogi." (Vivekananda, p.50).
This gets to be exciting stuff. What does Feuerstein, the great scholar of yoga, have to say? "In Yoga practice, breath control equals mental control. This formula is as fundamental as Einstein's E=mc² and as far reaching in its practical implications. It is through the proper regulation of the life force that the yogin can not only influence the nervous system and bodily functioning in general but also gain access to the subtle dimensions of existence by transcending the brain-dependent activities of the mind" (Georg Feuerstein, Shambhala Guide to Yoga, pp. 69-71).
Now, I don't know about you, but this just makes me want to sit right down and breathe! Don't worry about reaching enlightenment, just focus on your breath. Lengthen it. Deepen it. Listen to the sound it makes. Try to make your inhalations and your exhalation equal in length. That's all. Try that for five minutes a day and you will be off to a great start. Your chattery mind will settle right down. Any anxiety will be eased. Your blood pressure may drop. You will be experiencing the subtle control over your body's life force that you are capable of when you stop letting your mind be scattered by all the outside influences.