If you are referring to the volume of a cylinder, imagine a cylinder as a lot of circles stacked on top of one another. You know how to find the area of a circle. Now multiply that by the height of the cylinder.
I'm reminded of Edison, who took a graduate engineer into his lab. He asked the engineer to find the volume of a glass bulb. The graduate got out his calipers, and measured the dimensions of the bulb, then measured the thickness of the glass, then estimated the shape of the bulb as an ellipsoid with given axes, then set up a volume integration to do the mathematics. After an hour or two, eventually he came out with an answer: approximately etc. etc. Edison shrugged, filled the bulb with water, poured the water into a measuring glass and got a number which differed somewhat from that of the graduate.