What is Mantra
A mantra is a sequence of words or syllables that are chanted, usually repetitively, as part of a Buddhist practice.
Scholars consider mantras to be older than 1000 BC. The Chinese translation is zhenyan, 真言, which literally means "true words".
In Buddhism, mantras are sacred sounds that are believed to possess supernatural powers associated with Buddha or Bodhisattva. The Sanskrit word, mantra, consists of the root man- "to think" (also in manas "mind") and the suffix -tra, designating tools or instruments, hence a literal translation would be "instrument of thought".
One of the best known mantra is from Avalokitesvara Bodhisattva: The Six Character Great Bright Mantra - "Om mani padme hum". Tibetan Buddhists chant this mantra repeatedly as a part of meditation, often with the aid of mala beads for counting.
In Buddhism history, Buddha actually does not support the use of Mantra. If one is sick, one should find a doctor. If there is disaster, one should repent or do more positive things for the society. These teachings are based on the theory of Karma: good seed turns into tasty fruit; bad seed results with a unfavourable ending.
When Buddha entered into Nirvana, there are more varieties of people who become Buddhists, such as conjurers. Gradually Buddhism sutra starts to have records of Buddhists using mantra to cure patient's sickness. In fact, if one can constantly chant one mantra with full concentration and without alternative thoughts, this is similar to the practise of meditation, which is a way to quiet your body, mind and heart. Eventually, through the practise of chanting mantra, one will start to acknowledge or accept precepts, develop samadhi, otbtain inner wisdom and practise/deliver kindness. In this way, one is no longer being stubborn in the illusion and can have better connections with the Buddha and Bodhisattva.
In addition to use chanting mantra to control our random thoughts, chanting mantra is often used for the protection from evil and misfortune. They are chanted during large public rituals to avert collective danger and in private rituals to protect individuals against illness or other misfortune.