Gayatri Mantra

The Gayatri Mantra is one of the oldest, most powerful, and most revered hymns in Hindu scripture. Often called the "Mother of the Vedas," it is a universal prayer for enlightenment and wisdom that transcends religious and cultural boundaries.
In Sanskrit:
ॐ भूर्भुवः स्वः तत्सवितुर्वरेण्यं भर्गो देवस्य धीमहि धियो यो नः प्रचोदयात् ॥
Transliteration: Om Bhūr Bhuvaḥ Svaḥ Tat Savitur Vareṇyaṃ Bhargo Devasya Dhīmahi Dhiyo Yo Naḥ Pracodayāt

Word, Meaning
Om,The primordial sound of the universe.
"Bhūr, Bhuvaḥ, Svaḥ","The three planes of existence: Physical (Earth), Mental (Atmosphere), and Spiritual (Heaven)."
Tat,That (referring to the Supreme Reality).
Savitur,"The Sun God (Savitr), representing the source of life and light."
Vareṇyaṃ,"Adorable, worthy of worship."
Bhargo,Effulgence; the divine light that destroys sins and ignorance.
Devasya,Of the Divine.
Dhīmahi,We meditate upon.
Dhiyo,Intellect; the faculty of understanding.
Yo,Who / Which.
Naḥ,"Our (the prayer is collective, for everyone)."
Pracodayāt,"May inspire, enlighten, or guide."

Core Significance
The essence of the mantra is a humble request to the Divine to illuminate the intellect. It suggests that just as the physical sun removes darkness from the world, the spiritual "inner sun" should remove the darkness of ignorance from our minds, guiding us toward the path of righteousness (Dharma).
Benefits of Chanting
Mental Clarity: Regular recitation is believed to sharpen the intellect and improve concentration.
Stress Reduction: The rhythmic vibrations of the 24 syllables have a calming effect on the nervous system.
Spiritual Growth: It is considered a tool for self-realization and connecting with universal consciousness.
Purification: Traditionally, it is used to "burn away" past negative $karmas$ and purify the heart.
When and How to Chant
The most auspicious time is during Sandhya (the transition periods of the day):
Dawn: Facing the rising sun.
Noon: When the sun is overhead.
Dusk: Facing the setting sun.

It is traditionally chanted 108 times using a mala, but even chanting it 3, 11, or 21 times with focus and devotion is considered highly beneficial.