What are the functions of the id, ego, and superego?
The Id is basic instinct, parts of which are modified by experience to become the Ego (Self). The ego and id are moderated by the superego (morals).
The id ( the it) is the primitive and instinctive component of personality. The ego (the I) is 'that part of the id which has been modified by the direct influence of the external world' (Freud 1923). The superego (above I) incorporates the values and morals of society which are learned from one's parents and others.
Sigmund Freud's single most enduring and important idea was that the human psyche (personality) has more than one aspect. Freud (1923) saw the psyche structured into three parts (i.e. tripartite), the id, ego and superego, all developing at different stages in our lives. These are systems, not parts of the brain, or in any way physical.
McLeod, S. A. (2008). Id, Ego and Superego. Retrieved from www.simplypsychology.org/psyche.html
Freud, S. (1923). The ego and the id. SE, 19: 1-66.