Can you explain OM?

Om is considered as a sacred chant and a holy symbol. One can say Om in his mind while meditating. Om is also part of or beggining of various mantras. Ex: Om Namah Shivay (mantra for praying to lord shiva)
It is sacred like the cross for christians.
There are further deep meanings of the words 'OM'. You could research it, although its not necessary.

OM is considered a divine and holy sound. Actually in pranayama, that is breathing exercise, Oh stands for the deep air we bring out from our Nabhi(navel), Vu for, we are bringing that air upto our neck and Mmm for, we are closing our mouth and letting the air ie Carbon di oxide out through the nose. So, Oh + Vu + Mmm gives the sound OM, which has no caste, religion, and language. People of any caste, religion can say OM. Some people has the notion that it is a Hindu word. No. It is wrong. Since it is a divine word, Hindu temples will use this word at the top of the temple.

Om is the holy sound in Hinduism which is credited with being there when the world evolve. OM is the general pronunciation but many scriptures say it is AA + OO + AM, which can be pronounced as Aum. This is a word that takes precedence over any other word in ay other word in Hindu scriptures.

Any chant or mantra starts with Om. So in any situation Om is a word/chant to be done. The actual meaning has many interpretations, too many to be written about here. As one studies the scriptures one can go deep into the meaning and the philosophy.

You can take it as an all compassing chant to live a life of peace. Chant this in the deepest tone you can muster. You will draw all the benefits.

Om! shanti, shanti, shanti. Peace be to you all.

Om also spelt AUM: Briefly, bringing out the essential explanation given in the Mandukya Upanishad:- The A(pronounced as the 'u' as in but), the U is pronounced like the 'u' in put. The M is like the English M. The A represents ViShNu(= achyuta= Inseparable)the U represents Umesha(= Shiva= Goodness= Auspiciousness and UmeshaH= Lord of Uma(= Pure Intelligence). The 'M' repreents the entire Creation(= Brahmaa) that exists between the two points - the Moment of Creation and the moment of Destruction(more aptly Absorption).

OM is the Primordial Sound whence Creation began, and the reverberatory 'M' is the point of Absorption back into the Source. Such literal representaions are legion in the Vedantas and more so in the Tantras.

The right way of using Om as a mantra for meditation is to lengthen the 'O' as in go to, say, six seconds and then closing it with the reverberaory 'Mmmmm' for half the time i.e. 3 secs.

The significance of Om is that everything begins in the Primordial Sound= You could liken it to the Big Bang and the Silence after the completion of the reverberatory Mmmm.. Thus OM is the one-letter representation of Creation-Sustenance-Absorption back into The Source: ALL of Material presence. The Silence after and in between two successive OMs is as important as the way OM is "pronounced". Becuase it in the Silence that the Greatest Indescribable Truth is "Expressed". Is that oxymoronic for you?

P.S. If you are interested I could translate the whole of the Mandukya Upanishad(this is not a very big book) for you that "explains" OM from a Vedantic standpoint. Alternatively, you could read a translation of the same from say R.K. Mission and pose any queries you may have. Thanks for your interest in the subject, by explaining which I had a chance to meditate on this Essential Syllable.