The video discusses finding the area under a curve using rectangles with varying widths. By dividing the section into smaller sections (delta x), approximations for the area can be calculated by summing up the areas of the rectangles. As the number of rectangles (n) increases and the width of each rectangle (delta x) decreases infinitely, a more accurate approximation of the area can be achieved. The process involves considering the limit as n approaches infinity and delta x becomes infinitesimally small.