The process of chanting is nothing new. Those of us who grew up attending a church of some denomination (whether it be a Christian mass, a Jewish Shabbat, et cetera) are quite familiar with the back-and-forth repetition or reciting of hymnals. A large group of people in particular use these chanting methods to reach a form of transcendentalism, commonly referred to as "Om", "Ohm", or "Ahm" (which is typically how it is pronounced).
This type of rhythmic chanting, commonly seen state-side in Yoga classes and meditation parlors, is actually a practice that has been around since the early beginnings of Ancient Hindu religions. Om, generally speaking, is aspect of meditation where individuals chant a specific sound (oohhhmmmmmm), which helps to calm the mind by continuing to focus on a specific word or phrase. If you're familiar with Seinfeld at all, George's dad says "Goosfaba" in order to calm himself down. Invariably, it doesn't work. However, with proper practice, it can lead to a point of quiet being, less daily stress, and a potentially better outlook on day-to-day activities.
To better understand chanting and Om in general, taking a look at its roots is important. The practice of chanting for meditational purposes begins with ancient Hindu religion. The Hindu religion sees Om as a sacred sound and a spiritual icon. It is a way to reach what is known as transcendentalism", or a place of higher being. A mental state where, even the most aggressive of contrivances have no bearing or meaning on the physical world. Most refer to this state as "nirvana". Chanting helps one to achieve this state of being.
The practice of chanting is also commonly found in Hinduism, Buddhism, Jainism (an ancient Indian religion), and Sikhism (another, even older, Indian religion). Aside from ancient religions, chanting is commonly found in most modern yoga studios. In religions and yoga studios, the practice of chanting has a focus on the number three. When chanting, Om is separated into three syllables, with each syllable representing a different symbol: A - the past, H - the present, and M - the future. Chanting these will allow one to calm one's mind and focus on those three syllables and their respective meanings.
These chants also hold other meaning and value in other yoga circles. For some, the AHM focuses on the 3 divine powers: starting from creation to preservation and lastly the transformation. Even still, others who practice AHM chant in honor of the three essences of the spirit: omniscience, immortality and joy.
In the Hindu religion, Om is the representation Hindu Trimurti (the trinity of the most supreme divinity), and the union of the 3 gods, M for Shiva U for Vishnu and A for Brahma.
The origin of chanting Om is first mentioned in Upanishads (collection of ancient Sanskrit texts that contain some of the central concepts/ideals of Hinduism) and associated with the idea of "cosmic sound". It is also found in Aitareya Brajmana (collection of sacred Indian hymns) - three versions of the sound represent the three stages of cosmic creation and celebrated creation of universe. And, in early Upanishad and Vedic text, it refers to Om as a "tool for meditation"
In general, the idea behind practicing Om is for centering a person. It also helps to make stress go away, return the individual to a "perfect" or "pure" state through chanting, a.k.a. a mantra. Through practice and meditation, it is believed that a better, more carefree, and potentially healthier life.