Shamanism is an ancient ability. It is not a religion but has been perceived as one by those who mistakenly confuse it with Wicca, Witchdoctors or Wizards. The difference between Shamanism and the aforementioned is that Shamans do not worship the spirits. They commune with the spirits which is basically receiving helpful information from the spirits for the purpose of divination or healing. A true Shaman has respect for the Spirits and does not try to control them.
A Wiccan, Witchdoctor, Wizard or Witch may try to get the spirits to do their bidding and perform rituals or "magic" ceremonies to get the things they desire for personal gain or for paying clients.
Because of this confusion and fear that a Witch, Wizard, Warlock or even a Wiccan might be able to do, people and the church formed an all out witch hunt and inquisition to torture, burn and kill all suspects of this discipline. People did not want to take a chance that any spirits harm them or cause there crops to fail or any number of unexplainable things so they decided that any communication with spirits was a bad thing and made it a mission for centuries to rid the earth of all people suspected or capable of communing with spirits.
In time, Shaman's seemed to disappear from the world for any who were foolish enough to admit being a Shaman was to invite persecution from the church and fear from the community. There were good Shaman and bad Shaman, good Witches and bad Witches, good Warlocks and bad Warlocks. The ability could vary from person to person but so could the person's agenda and motive.
Some of the abilities and duties of the Shaman were first and foremost to protect and serve there community. If a bad Winter was coming the Earth Shaman would warn the community so they could stock extra food and wood. If an invasion was coming the Shaman would tell everyone so they could move or prepare to fight. The Shaman depended heavily upon the spirits for survival. In the spiritual world, time ceases to exist. The Spirits know the past and future. The Shaman know this and can go to the Spirits for help if a disaster can be avoided or if a new resource can be found the spirits know when and where. In the spiritual world the Shaman can communicate with the spirits of the animals, plants and elements and if permission is granted they will tell the Shaman what he needs to know to help his people or community. Some examples of this would be the earth spirit knows where the healing plants grow. Communing with this spirit guides the Shaman to those plants to help heal sickness or injury. The animal spirit knows where the animals are. If permission is granted the animal spirit tells the Shaman where to find game and where the hunters should go to hunt to feed the community. This is the core purpose of Shamanism.
A Wiccan is a white Witch. The Wiccan understands that there is a spirit or many spirits in nature and seeks to pay homage to these spirits and seasons. Rituals are usually performed during certain seasons or equinoxes during the year. The Wiccan is a feminine aspect and may homage to the female goddess within all Women.
A black Witch, (negative connotation), Sorcerer, Sorceress, Wizard etc., were the disciplines that the Church and the Ancient Civilizations were most concerned with and feared. They might use a negative means to get a result. These things might include hypnosis, trickery, persuasion, lies, sacrifices, rituals, magic, herbs, brews, worshiping or whatever it took or whatever they thought it took to get a result.
Because Shaman, Witches, Wizards, Warlocks, Sorcerers and the like all work with or understand the nature of spirits it was easy for people to get confused but no matter what the discipline it really comes down to the person of the discipline. If they seek to achieve a positive outcome using harmless or positive methods then no harm is done. If they seek to achieve a positive outcome (in there opinion or there clients) using negative, illegal or harmful methods then one should be wary and cautious in the company of said individual.
When one is dealing with spirits there is an absolute rule that should always be obeyed. That is to never command the spirits to do your bidding. (This is different from asking a question or seeking information) and to never bend to the will of a spirit unless it Jesus or God himself. The spiritual world is a reflection of the physical world in some respects and it really is about respect.