In order to explain channelling, it is perhaps best to define the word itself. In a physical sense, channelling is the forming of a connection between two points in order to enable a flow, for example of water or electricity, between the two. In a psychic sense, it is the connection made from the physical to the spiritual world through a channeller or medium, as they are frequently referred to.
A message or communication is received from a specific spirit - this can be an entity who used to inhabit a physical body or an entity who claims never to have inhabited a body - and passed on, either in written or spoken form, as though it is the spirit him/ herself speaking. An entity currently within a body may also be channelled, although this is not usually what is meant.
Contact is made either through telepathy, which many regard as a more refind kind of subtle verbal communication (this type is two-way and things being said are usually open to interpretation), or spirit direct to body contact, where the spirits enters, or at least partly controls, the body of the person forming the connection. Occasionally both ways are used.
There are many different methods of establishing this communication link, depending on each individual. To go into each one in intricate detail would take up a book, but as a whole, it can be divided into three main groups, or states of consciousness.
Some will form this connection in a fully conscious state, meaning they are fully aware of what is going on and are able to move about or stop and start without any noticable interruption in the flow of communication.
Others will enter an altered, or superconscious, state. This differs from being fully conscious in that the focus is slightly off and although the individual seems to be aware, it may be difficult to recall aspects or concepts which were clear at the time with clarity afterwards.
Another option is for the individual to enter either a light (staying still partially aware) or a deep trance. The entity will then take over and either telepathically or through entering the body convey the particular message/ s. Here, the individual may not remember any of what occurred during the session.
Whichever way or method is chosen is very much up to the preference and ability of each individual, there is no right or wrong way. Messages come with varying clarity (depending again on the individual, the entity involved and various other circumstances), are open to interpretation and should be approached with an open mind - although a messages may seem to be irrelevant at the time, it may make perfect sense on reflection.
It must be said that any entity wanting to communicate has to be invited by the individual to do so. If the individual is not happy with the approach, energy or message conveyed from an entity, they may ask it to leave and it will have to comply.