The mantra, Om, actually consists of three letters: A, U and M. Each of these three parts serve have universal elements of reality which are not easily discovered or experienced in our everyday life. The A is pronounced "ah" and represents our waking state, which is also the subjective consciousness of the outer world. The U, which is pronounced "ooh", is the dreaming state, or the consciousness of our inner world of thoughts, dreams, and memories. While the M is the dreamless state of deep sleep and the experience of ultimate unity. When we chant this sacred sound, it is said that our consciousness become prepared for meditation. The vibration slowly dissolves into silence, or the transcendent state of consciousness.
Many people are uncomfortable chanting when they first begin their yoga practice. I know I definitely was. It wasn't till I understood the importance behind it, the sense of community that comes with creating a vibrational sound together, that I realized how necessary this part of yoga is. Practicing elongating your breath helps when chanting Om. And with time, this mantra becomes part of your practice, part of you, part of the entire world.
After all, Om is considered the eternal sound - the sound of the Universe or of creation. There was research done where they recorded the sound Om, put it into the computer and found that the frequency of Om is exactly the same as the frequency of earth’s rotation around its own axis. So, in some sense, you could say that the earth is saying Om. This mantra has metaphysical associations. It is the sound of consciousness and brings your awareness within.