The sound itself sounds like a short "a" (AH). This is a very powerful sound and it is found in all words of power. God, Jehovah, Allah, and Buddha are just a few examples of the God Sound. The God Sound should not be confused with the mystical chant OHM, which is very different.
This meditation technique can be done at anytime. It is very useful as a calming practice. Your eyes can be open or closed, although you will probably prefer to close them if you can. Clear your mind and take a deep breath. On your exhale voice a long drawn out AH. You will feel the vibrations resonate deeply throughout your body. When you are out of breath inhale again deeply and repeat the process.
It only takes three or four repetitions in order to feel the deep calm that follows this discipline. It is a good prelude to a deeper meditation practice. If someone throws you off balance and you feel anger growing inside of you take a few moments and try this technique. You will find it is far more effective than counting to ten.
In addition to calm the God Sound is also good at aligning your psychic energies. A few moments of this practice and you will charge your intuition and insights. Performing it before sleep focuses the mind and precognitive dreams may be the result.