The following is taken from here:
The self is the most important personality archetype and also the most difficult to understand. Jung has called the self the central archetype, the archetype of psychological order and the totality of the personality. The self is the archetype of centeredness. It is the union of the conscious and the unconscious that embodies the harmony and balance of the various opposing elements of the psyche. The self directs the functioning of the whole psyche in an integrated way. According to Jung, "[C]onscious and unconscious are not necessarily in opposition to one another, but complement one another to form a totality, which is the self" (1928b, p. 175). Jung discovered the self archetype only after his investigations of the other structures of the personality.
The self is depicted in dreams or images impersonally (as a circle, mandala, crystal, or stone) or personally (as a royal couple, a divine child, or some other symbol of divinity). Great spiritual teachers, such as Christ, Muhammed, and Buddha, are also symbols for the self. These are all symbols of wholeness, unification, reconciliation of polarities, and dynamic equilibrium--the goals of the individuation process (Edinger, 1996).
Jung explains the function of the self: The ego receives the light from the Self. Though we know of this Self, yet it is not known.... Although we receive the light of consciousness from the Self and although we know it to be the source of our illumination, we do not know whether it possesses anything we would call consciousness.... If the Self could be wholly experienced, it would be a limited experience, whereas in reality its experience is unlimited and endless.... If I were one with the Self I would have knowledge of everything, I would speak Sanskrit, read cuneiform script, know the events that took place in pre-history be acquainted with the life of other planets, etc. (1975, pp.194-195)
The self is a deep, inner, guiding factor, which can seem to be quite different, even alien, from the ego and consciousness. "The self is not only the centre, but also the whole circumference which embraces both conscious and unconscious; it is the centre of this totality, just as the ego is the centre of consciousness" (1936b, p. 41). It may first appear in dreams as a tiny, insignificant image, because the self is so unfamiliar mid undeveloped in most people. The development of the self does not mean that the ego is dissolved. The ego remains the center of consciousness, an important structure within the psyche. It becomes linked to the self as the result of the long, hard work of understanding and accepting unconscious processes.
Edinger, E. (1996). The Aion lectures. Toronto: Inner City Books.
Jung, Carl. The relations between the ego and the Unconscious. In Collected works (Vol. 7). (Originally published, 1928b.)
------. Individual dream symbolism in relation to alchemy. In Collected works (Vol. 12). (Originally published, 1936b.)
-------. (1975). Letters, Vol. 11: 1951-61. (G. Adler, Ed.). Princeton, NJ: Princeton University Press.