How to describe?
Shamanistic traditions have existed worldwide since prehistoric times.For shamanism the visible world is pervaded by invisible forces or spirits that affect the livings. Shaman stands for "he/she who knows" A similar word in Sanskrit "shamana" means the act of calming, tranquilizing, soothing but also destroying. It has replaced the term “witch doctor”, a term which unites the two stereotypical functions of the shaman: knowledge of magic and ability to cure a person or mend a situation.
Shamans are working by forming a special relationship with, or gaining control over spirits.
It is said that in cooperation with “their” spirits they can control the weather, can use divination, can interpret dreams, execute astral projections and travel to upper and lower worlds. They are the experts employed by animists or animist communities.It is not, however, often organized into full-time ritual or spiritual associations, as are priests.

Shamanism today
Today, shamanism, once universal, survives mainly among indigenous peoples. While concentrated in the tundras, jungles, deserts and other rural areas worldwide in a lesser extend Shamans can be found also in cities, towns, suburbs, and shantytowns all over the world. This is especially widespread in Africa and South America.
Efforts have been made to link shamanic practice and knowledge with Western, scientific beliefs. Some researchers proposed that shamans take their consciousness down to the molecular level, working with DNA and viruses that they see as the twin serpents or malicious "darts". The holomovement theory proposed by others is often seen as an approach to create a scientific foundation for concepts such as parallel worlds and alternative ways to traverse time and space.
At the present time the term Shaman is generally considered to be anthropologically inaccurate. and the term “Medicine man” is preferred, especially as not all traditional peoples approve of the use of shaman as a generic term, given that the word comes from a specific place and people.
In Nepal Shamanism is mainstream. It exists alongside medicine as a viable healing system. Shamans are consulted by kings, priests, and laymen alike for healing, divination and as intermediaries with the spirits. The ancient wisdom tradition of Tibetan and Nepalese shamans is passed on through pilgrimage type full-moon initiations in which shamans transmit power (sakti) for the healing of self and the prosperity of the community.

History
Shamanistic date back to the Neolithic period. Aspects of shamanism are encountered in later, organized religions, generally in their mystic and symbolic practices.
Greek paganism was influenced by shamanism, as reflected in the famous stories of Tantalus, Prometheus and Medea, as well as in the Eleusinian and other mysteries. Some of the shamanic practices of the Greek religion were later adopted into the Roman religion.
The shamanic practices of many cultures were marginalized with the spread of Christianity.
The repression of shamanism continued with the Spanish colonization of the Caribbean, and Central and South America, when Catholic priests followed the Conquistadors and were instrumental in the destruction of local traditions. In North America, the English Puritans conducted periodic campaigns against individuals perceived as witches.
In Asia one can find a strong shamanistic influence in the Bön religion of central Asia, and in Tibetan Buddhism. Buddhism became popular with shamanic peoples such as the Tibetans, Mongols and Manchu beginning in the eighth century. Forms of shamanistic ritual combined with Tibetan Buddhism became institutionalized as state religion under the Chinese Yuan and Qing dynasties.
According to some, one common element of shamanism and Buddhism is the attainment of spiritual realization, at times mediated by psychedelic substances. However, in the shamanic cultures still practiced by various ethnic groups in Nepal and northern India, shamans are not necessarily considered enlightened, and often are even feared for their ability to use their power to carry out malicious intent.

In the Native American groups of North America only the shaman had the power to commune with the gods or spirits, to mediate between them and ordinary mortals, to talk with the souls on behalf of the living. The shaman, man or woman, was often an extraordinary character, both in physical appearance and in acting talents. He would be a mystic, poet, sage, healer of the sick, guardian of the tribe, and the repository of stories. Those who did not possess the full range of the shamanistic attributes became "medicine men", and functioned as respected healers.

How to become a Shaman?
While a “normal” priest is a ceremonially inducted member of a recognized religion, where he holds a certain rank and functions as the tenant of an office, the shaman is one who through a personal psychological crisis, has gained a certain power of his own.
A shaman may be initiated via a serious illness, by being struck by lightning, or by a near-death experience. There is usually a set of cultural imagery expected to be experienced during shamanic initiation regardless of method. Such imagery often includes being transported to the spirit world and interacting with beings inhabiting it, meeting a spiritual guide, being devoured by some being and emerging transformed, often with implanted amulets such as magical crystals. The imagery of initiation generally speaks of transformation and granting powers, and often entails themes of death and rebirth.
In some societies shamanic powers are considered to be inherited, whereas in others shamans are considered to have been "called": Among the Siberian Chukchis one may behave in ways that Western clinicians would characterize as psychotic, but which Siberian culture interprets as possession by a spirit who demands that one assume the shamanic vocation. Among the South American Tapirape shamans are called in their dreams. In other societies shamans choose their career:

Healing
The shaman plays the role of healer in shamanic societies; shamans gain knowledge and power by traversing the axis mundi and bringing back knowledge from the heavens. Often the shaman has, or acquires, one or more familiar helping entities in the spirit world; often spirits in animal form, spirits of healing plants, or sometimes departed shamans.
While the causes of disease are considered to lie in the spiritual realm, being effected by malicious spirits or witchcraft, both spiritual and physical methods are used to heal. Commonly, a shaman will "enter the body" of the patient to confront the spirit making the patient sick, and heal the patient by banishing the infectious spirit. Many shamans have expert knowledge of the plant life in their area, and an herbal regimen is often prescribed as treatment.
In many places shamans claim to learn directly from the plants, and to be capable of harnessing their effects and healing properties only after obtaining permission from its abiding or patron spirit. In South America, individual spirits are summoned by the singing of songs called icaros; before a spirit can be summoned the spirit must teach the shaman its song. The use of totem items such as rocks is common; these items are believed to have special powers and an animating spirit. Such practices are very ancient
The shaman usually enjoys great power and prestige in the community, and is renowned for their powers and knowledge; but they may also be suspected of harming others and thus feared.
By engaging in this work, the shaman exposes himself to significant personal risk, from the spirit world, from any enemy shamans, as well as from the means employed to alter his state of consciousness. Certain of the plant materials used can be fatal, and the failure to return from an out-of-body journey can lead to physical death. Spells are commonly used to protect against these dangers, and the use of more dangerous plants is usually very highly ritualized.

The Shaman approaches his healing way by entering into an ecstatic trance, either autohypnotically or through the use of entheogens. The methods used are diverse, and often are used in conjunction with each other. Some of the methods for effecting such altered states of consciousness are: Drumming , Singing, Fasting , Sweat lodge, Vision quests, Dancing and others.
Normal is the use of "power plants" such as: Tobacco,Fly Agaric,Psychedelic Mushrooms Alluded to euphemistically as "holy children" by Mazatec shamans or Andean natives
Shamans often observe special diets or fasts and taboos particular to their vocation. Sometimes these have physical purposes beyond effecting a change in brain state or taboo; for example, the diet followed by shamans and apprentices when drinking Ayahuasca includes eating foods rich in tryptophan (which produces serotonin) as well as avoiding foods rich in tyramine, which could cause a hypertensive crisis if ingested with a Maoi such as Ayahuasca.

Gender and sexuality
Most shamans are men, but there are societies in which women may be shamans.
In some societies, shamans exhibit a two-spirit identity, assuming the dress and attributes of the opposite sex from a young age, for example, a man taking on the role of a wife in an otherwise ordinary marriage. Such two-spirit shamans are thought to be especially powerful. They are highly respected and sought out in their tribes, as they will bring high status to their mates.

Shamanism and New Age movement
The New Age movement imported some ideas from shamanism as well as Eastern religions. As in other such imports, the original users of these ideas frequently condemn New Age use as misunderstood and superficial.
At the same time, there is an endeavor in occult and esoteric circles to reinvent shamanism in a modern form, drawing from core shamanism, a set of beliefs and practices synthesized and often revolving around the use of ritual drumming and dance.
Various indigenous forms of shamanism often focus on the ritual use of entheogens; as well as chaos magic. Much of this is focused upon in Europe, where ancient shamanic traditions were suppressed by the Christian church and where people compelled to be shamans often find it improper to use shamanic systems rooted in other parts of the earth. Various traditional shamans express respect for this endeavor, sharply distinguishing it from "light" New Age shamanism. Some anthropologists and practitioners have discussed the impact of such 'neo-shamanism' as 'giving extra pay' to indigenous shamanisms, particularly as many pagan- or heathen-'shamanic practitioners' call themselves by specific names derived from older European traditions. Sometimes people from Western cultures claim to be shamans (i.e., Wicca, Neo-Paganism). This is considered offensive by many indigenous medicine men, who view these New Age, western "shamans" as hucksters out for money or affirmation of self. Many shamanistic cultures feel there is a danger that their voices will be drowned out by self-styled "shamans," citing, for example, the fact that some western authors have sold more books than all Native American authors put together.