The Id is irrational, instinctual, and uncaring while the Super Ego is paralyzed with the pressures of society. These two sides of our psyche are in a constant battle as we make even the smallest decision during our day.
The Ego is the part of our mind that deals with reality. It is the middle ground between our instinctual reactions and the expectations of the world around us. Our Ego strives to satisfy the needs of our Id while still complying with the basic rules of society. For example, the Ego allows us to resist the urge to grab other people's belongings and buy them instead.
The Ego helps us organize our thoughts and react to daily life in a socially acceptable way. Think of the common cartoon scenes of an angel on one shoulder and a devil on the other. This isn't to say that Id and Super Ego are good and evil, but there are two sides of your psyche that are constantly battling for attention. It is the middle man's job to listen to both and find the happy medium.
The Ego is similar to common sense. It satisfies the desire of the Id while still paying attention to society's rules that the Super Ego stresses about.