Think of a wine barrel. Johannes Kepler once tried to calculate its volume by imagining the wine was made of infinitely many, infinitely thin disks stacked on top of each other. By "summing" the areas of all those thin disks, he found the volume of the whole container.
Long ago, math was mostly about straight lines and simple shapes. You could easily find the area of a square or a triangle. But as civilizations grew, they needed to measure things that curved—like the area of a circular field or the volume of a rounded wine barrel. Introduction to integral Calculus
Centuries later, in the 1600s, Gottfried Wilhelm Leibniz and Isaac Newton independently discovered that integration was actually the "undoing" of differentiation. While differential calculus looks at the (like how fast a car is going right now), integral calculus looks at the accumulation (how much distance the car has covered in total). Think of a wine barrel