What do id, ego and super-ego exactly mean?
You are pretty much on the money with your description, but here is some further information to help understand the definitions:

Paraphrased from "Freud's Structural and Topographical Models of Personality" (allpsych.com):

The id is what we are born with, it is the mechanism that allows our basic needs to be met, and is with us from birth. Essentially, the part of the brain that 'cares' only about it's own satisfaction and needs.

The ego meets the needs of the id, while taking into consideration the reality of the situation (e.g. needs of others).  According to Freud, this is the strongest part, meeting the needs of the id, while not upsetting the superego.

The superego is the moral part of our psyche, that deals with the ethical and moral constraints, i.e. belief in what is right and wrong.

Edited to add: Further and more detailed information can be found included from page 5 in this article from the University of Notre Dame "Id, Ego, and Superego" (Lapsley and Stey).