The formula "A = l × w" is used to calculate the area A of a rectangle. In this equation, l represents the length of the rectangle, while w stands for the width. By multiplying these two dimensions together, you can find out how much space is contained within the rectangle. For example, if a rectangle has a length of 5 units and a width of 3 units, you would calculate the area by multiplying 5 by 3. This gives you an area of 15 square units, indicating the total surface area of the rectangle.