When you go to a Buddhist temple you may encounter people chanting. All schools of Buddhism have some kind of chanted liturgy, although the content of the chants varies widely.
Newcomers are sometimes uncomfortable with chanting. We may come from a religious tradition in which a standard text is recited or sung during a worship service, but we don't often chant. Further, in the West many of us have come to think of liturgy as a pointless vestige of an earlier, more superstitious, time.
During the chanting service you may see people bow or play gongs and drums. Priests may make offerings of incense, food and flowers to a figure on an altar. The chanting may be in a foreign language, even when everyone attending speaks English. That can seem very strange. Isn't Buddhism supposed to be nontheistic?
However, once you understand what's going on you may see that Buddhist liturgies actually serve a useful purpose -- not to worship a god, but to help us realize enlightenment. Enlightenment (bodhi) is awakening from one's delusions, especially the delusions of the ego and of a separate self. This awakening is not intellectual, but a change in how we experience and perceive. Think of mindful chanting as a tool for helping you wake up.
For further explanation of how rituals and liturgies function in Buddhism, please see "Ritual and Buddhism: The Purpose of Rituals in Buddhism."
Types of Buddhist Chants
There are several different types of texts that are chanted as part of Buddhist liturgies. Here are a few:
The chant may be all or part of a sutra (also called a sutta). A sutra is a sermon of the Buddha or one of the Buddha's disciples. However, a large body of sutras of Mahayana Buddhism actually were composed after the Buddha's lifetime. (See also "Buddhist Scriptures: An Overview" for more explanation.)
A mantra is a short sequence of words or syllables, often chanted repetitively, thought to have transformative power. An example of a mantra is om mani padme hum, which is associated with Tibetan Buddhism. Chanting a mantra mindfully can be a form of meditation.
A dharani is something like a mantra, althugh usually longer. Dharanis are said to contain the essence of a teaching, and repetitive chanting of a dharani may evoke some beneficial power, such as protection or healing. Chanting a dharani also subtly affects the mind of the chanter. Dharanis usually are chanted in Sanskrit (or some approximation of what Sanskrit sounds like). Sometimes the syllables have no definite meaning; it's the sound that matters.
A gatha is a short verse to be chanted, sung, or recited. In the West, gathas often have been translated into the language of the chanters. Unlike mantras and dharanis, what gathas say is more important than what they sound like.
There are some chants that are exclusive to particular schools of Buddhism. The Nianfo (Chinese) or Nembutsu (Japanese) is the practice of chanting the name of Amitabha Buddha, a practice found only in the several Pure Land forms of Buddhism. Nichiren Buddhism is associated with the Daimoku, Nam Myoho Renge Kyo, which is an expression of faith in the Lotus Sutra. Nichiren Buddhists also chant Gongyo, consisting of passages from the Lotus Sutra, as part of their daily formal liturgy.
How to Chant
If you are new, the best advice is to listen carefully to what everyone around you is doing, and do that. Pitch your voice to be in unison with most of the other chanters (no group is every completely in unison), copy the volume of the people around you, and start chanting.
Chanting as part of a group service really is something you are all doing together, so don't just listen to yourself chant. Listen to everyone at once. Be part of one big voice.
Very probably you will be given the written-out text of the chanting liturgy, with foreign words in English transliteration. (If not, then just listen until you catch on.) Treat your chanting book respectfully. Be mindful of how other people are holding their chanting books, and try to copy them.
Translation or Original Language?
As Buddhism moves West, some of the traditional liturgies are being chanted in English or other European languages. But you may find a substantial amount of liturgy is still chanted in an Asian language, even by non-ethnic Asian westerners who don't speak the Asian language. Why is that?
For mantras and dharanis, the sound of the chant is as important, sometimes more important, than the meanings. In some traditions the sounds are said to be manifestations of the true nature of reality. When chanted with great focus and mindfulness, mantras and dharanis can become a powerful group meditation.
Sutras are another matter, and sometimes the question of whether to chant a translation or not causes some contention. Chanting a sutra in our own language helps us internalize its teaching in a way mere reading cannot. But some groups prefer to use Asian languages, partly for the effect of the sound and partly to maintain a bond with dharma brothers and sisters around the world.
Chanting may still seem a silly waste of time for you. But you never know, going forward, what will open the door. Many times I've heard senior students and teachers say that the thing they found most tedious and foolish when they first began to practice was the very thing that triggered their first awakening experience. So please don't knock it if you haven't at least tried it.