The superego makes up a large part of our unconscious. It is the part of us that makes us conform to particular rules, that makes us "behave." It judges us, criticizes us, and makes us feel bad when we do something "wrong." It is what makes us feel guilty and ashamed. It is our "inner critic" or "inner judge."
Our superego tells us things like that we shouldn't break things, not be rude to people, and say "please." It tells us which ways to sit, walk and talk are not appropriate. It tells us not to be lazy, to be cooperative and that we should do like we're told.
It judges us for whether or not we conform to the rules. Next to making us feel guilty and ashamed, it makes us feel stupid, idiotic, foolish, thick, dense, and a loser. That is, if we do not suppress these painful feelings.
While the superego has our best interest in mind, it is not a friendly character.
We usually hardly notice the superego controlling us. We just "know" we shouldn't do certain things, and we shy away from them, or we just know that we "must" do things. Most of it is, in fact, unconscious.
Formation of the superego
Most of the superego is formed during our upbringing. Our parents taught us what is right and wrong, what we should and shouldn't do, what is normal and what not. To get us to accept the rules, we were forced in various subtle and not so subtle ways, like by punishment, being shamed, or being degraded for doing something wrong. This is what's formed into the superego.
It's not only our parents, but, in fact, many other people too in our early environment that pressured us to abide by certain rules. Adults in positions of authority, as well as other children. And people still pressure us to when we are adults, when they act out their superegos on us, as we do on them.
The superego is kind of the sum of all people that have tried to make us behave according to certain rules in the past.
The need for the superego
Children aren't much capable of themselves to see the consequences of their actions. They need to be taught to abide by certain rules, or else they or others get hurt or worse, things get damaged, or things go wrong. They need to be taught to take responsibility.
Therefore, it is unavoidable and beneficial that children develop a superego. There is a need for it to be a guide through people's lives.
When the superego works against us
Sometimes we feel that we are guilty of something, when in truth there is nothing wrong with what we did. We may feel guilty for being lazy, when there really is no work to do. We can feel stupid for not knowing how to do something, when we never actually had an opportunity to learn it. Children are known to feel irrationally guilty for the death of relatives, or for parents divorcing.
Sometimes we need to be assertive, like when sales people or telemarketers intrude on us and treat us manipulatively. But if they seem nice, which they usually make great efforts to, we are inclined not to assert ourselves, because our superego stops us from being rude.
The superego isn't particularly precise. It may tell us not to do certain things when there is objectively nothing wrong with doing them. Thus, it is an aspect of us that can limit us more than necessary.