Okay kiddo, have you ever seen a soup can or a soda can? They are shaped like a cylinder, which means they have a round top and bottom and straight sides. Now imagine you have a group of these cans all stacked up together. They would make a cylinder set.
Now, if we want to measure this cylinder set, we need to figure out a few things. First, we need to know how wide it is across the top and bottom. We call this the diameter. Next, we need to know how tall it is. We call this the height.
Once we have these measurements, we can calculate the volume of the cylinder set. To do this, we use a special formula. You don't need to worry too much about the math, but basically we multiply the diameter by itself (that's what we call "squaring" it) and then multiply that by 3.14. Then we multiply that answer by the height.
The volume tells us how much space the cylinder set takes up. So if someone asks you how big a cylinder set is, you can tell them the diameter and height, and maybe even the volume if you're feeling really fancy!