Attempts to communicate with the dead and other living human beings, aka spirits, have been documented back to early human history. The story of the Witch of Endor (In the most recent edition of the NIV witch is rendered medium in the passage) tells of one who raised the spirit of the deceased prophet Samuel to allow the Hebrew king Saul to question his former mentor about an upcoming battle, as related in the Books of Samuel in the Jewish Tanakh (the basis of the Old Testament).
What actually transpires during the trance is that the clairvoyant medium sees visions, hears voices, feels the energy and interprets his experiences in intelligible human language. The narration of the sequence of events is convincing as it divulges the secrets and facts, which are known only to the seeker. This revelation of personal facts builds trusts between the seeker and the clairvoyant medium.
^ Joseph McCabe. (1920). Spiritualism: A Popular History from 1847. Dodd, Mead and Company. pp. 110–12. A Mr. Merrifield was present at one of the sittings. Home's usual phenomena were messages, the moving of objects (presumably at a distance), and the playing of an accordion which he held with one hand under the shadow of the table. But from an early date in America he had been accustomed occasionally to "materialise" hands (as it was afterwards called). The sitters would, in the darkness, faintly see a ghostly hand and arm, or they might feel the touch of an icy limb. Mr. Merrifield and the other sitters saw a "spirit-hand" stretch across the faintly lit space of the window. But Mr. Merrifield says that Home sat, or crouched, low in a low chair, and that the "spirit-hand" was a false limb on the end of Home's arm. At other times, he says, he saw that Home was using his foot." https://drive.google.com/file/d/1PpwyDe2ua5cGzC26TAXnYrB9K-K6WVEp/view?usp=sharing
In 1910 at a séance in Grenoble, France the apport medium Charles Bailey produced two live birds in the séance room. Bailey was unaware that the dealer he had bought the birds from was present in the séance and he was exposed as a fraud.[114] The psychical researcher Eric Dingwall observed the medium Bert Reese in New York and claimed to have discovered his billet reading tricks.[115] The most detailed account at exposing his tricks (with diagrams) was by the magician Theodore Annemann.[116]
A clairvoyant medium is a psychic who goes into trance, a sleep like state in which he allows his body and senses to be possessed by the spirit which may be his own guiding spirit or that of the seeker. The spirit has an overview of all the happenings on the earth. A clairvoyant medium can speak while lying down. He can also sit down or even walk and make gestures by moving his hands. He can even write or type his messages.
The magician Samri Baldwin exposed the tricks of the Davenport brothers in his book The Secrets of Mahatma Land Explained (1895).[93] The medium Swami Laura Horos was convicted of fraud several times and was tried for rape and fraud in London in 1901. She was described by the magician Harry Houdini as "one of the most extraordinary fake mediums and mystery swindlers the world has ever known".[94]
It's important to know that the free psychic chat rooms are not for receiving free readings. The free chat rooms are for you to get to know the psychics before you invite them for a private reading. But that being said, it is totally possible to get a free answer or free reading during a free chat. There are many psychics who offer totally free psychic answers on a regular basis. 
Today "demonstration of mediumship" is part of the church service at all churches affiliated with the National Spiritualist Association of Churches (NSAC) and the Spiritualists' National Union (SNU). Demonstration links to NSAC's Declaration of Principal #9. "We affirm that the precepts of Prophecy and Healing are Divine attributes proven through Mediumship."

^ "Glossary of Key Words Frequently Used in Parapsychology" Archived 2010-12-24 at the Wayback Machine, Parapsychological Association website. "Materialization: A phenomenon of physical mediumship in which living entities or inanimate objects are caused to take form, sometimes from ectoplasm." Retrieved January 24, 2006 "Medium – Definition". Dictionary.com. Retrieved 23 March 2007.