There is a mantra called the Gayatri mantra, which is considered the most powerful.
It is said that Hindus receive a sacred object from a guru through an initiation ceremony, and they receive it with reverence and quietly chant it.
The version that is famous is the one by Sai Baba. It seems there are various variations in terms of tempo and intonation.
ॐ भूर्भुवः॒ स्वः । |
oṃ bhūr bhuvaḥ svaḥ |
Tat savitur varenyam. |
tat savitur vareṇyaṃ |
Bhargo devasya dhimahi. |
bhargo devasya dhīmahi. |
May that intellect inspire us. |
May [the goddess] Saraswati enlighten our intellect. |
Another version.
Mantras are originally not supposed to be chanted by people other than those who have undergone initiation in Hinduism. Only shlokas are meant to be chanted by anyone.
The following is a brief summary of the meanings, for my reference.
ॐ Bhūrbhuvaḥ. Self. ।
| ॐ | om |
Holy sound Ohm.The fundamental principle of the universe, Brahman. |
भूर् |
bhūr |
The self-existence of God, prana, and life. |
Bhuv : |
bhuvaḥ |
The absolute consciousness of God, the relationship with the heavenly world, and the role of God in removing all pain and suffering (Apaana). |
स्व : |
svaḥ |
The all-pervading nature that is filled with everything, the divine bliss. |
Tat savitur varenyam. ।
| तत् | tat |
In Sanskrit, "that" refers to the third person. It means selfless. It implies the meaning of being selfless and without desire. Here, it means "that (god)." |
Savitur. |
savitur |
A spring that gushes forth. A god who is the source of all things that exist. |
Varenyam. |
vareṇyaṃ |
God's acceptance. |
Bhargo. devasya धीमहि ।
| Bhargo. | bhargo |
The glorious light of God's love and power. |
Of the god. |
devasya |
God. The multifaceted reality of God's absolute nature. |
धीमहि |
dhīmahi |
Meditation and focusing our minds on God. |
dhio Yo. नः॑ prachodayāt ॥
| धीयो | dhiyo |
Sanskrit: "intelligence". |
Yo. |
yo |
"Someone (who)" or "That (that)". |
N: |
naḥ |
It is something that belongs to all of us (all of humanity). |
प्रचोदयात् |
pracodayāt |
Please provide it. |
Reference:
Gayatri Mantra – Wikipedia
https://ja.wikipedia.org/wiki/%E3%82%AC%E3%83%BC%E3%83%A4%E3%83%88%E3%83%AA%E3%83%BC%E3%83%BB%E3%83%9E%E3%83%B3%E3%83%88%E3%83%A9
【Mantra】: Gayatri Mantra: Part 1: Translation and Explanation | Indian Astrology.com Blog
http://indian-vedic-astrology.com/brog-1/2015/01/18/%E3%80%90%E3%83%9E%E3%83%B3%E3%83%88%E3%83%A9%E3%80%91%EF%BC%9A%E3%82%AC%E3%83%A4%E3%83%88%E3%83%AA%E3%83%BC%E3%83%BB%E3%83%9E%E3%83%B3%E3%83%88%E3%83%A9%EF%BC%9A%E3%81%9D%E3%81%AE1/ Gayatree Mantra's alternative: Shloka and detailed meaning
http://hindu-dharma-japan.blogspot.jp/2015/03/gayatrisloka.html