Clairvoyance means Clear seeing, this includes being able to see spirit entities, either as physical manifestation (as though live humans were standing by the side of you), or vividly with the minds eye (as though watching a film).
Receiving spirit messages is not always as easy as it sounds. Spirits often communicate using symbols, so the clairvoyant has to interpret and analyse what they mean before passing on the message. For example if the medium is shown a row of flower pots, the meaning has to be deciphered before the message will make sense to the client, e.g. are they referring to the name Potts, or the person was a keen gardener, or even a potter?