This video explains to you how to find the area of a square.
The area of a square is given by the formula
area = width x height
But since the width and height are by definition the same, the formula is usually written as
area = s x s
where s is the length of one side.
In strictly correct mathematical wording the formula above should be spoken as "s raised to the power of 2", meaning s is multiplied by itself. But we usually say it as "s squared". This wording actually comes from the square. The length of a line s multiplied by itself, creates the square of side s. Hence "s squared".