Okay kiddo, let me tell you about a compression member.
You know how when you push something, like a stuffed animal, with your hands it squishes down, right? Well, imagine something that can take a lot of pushing, like a big, strong pencil or a wide, flat ruler.
If you push down on the top of the pencil or the ruler, it will bend a little bit, but it won't break. This is because it's designed to take that kind of pressure, and it's called a compression member.
Compression members are found in all kinds of things, like bridges and buildings. They help to support the weight of the structure and keep it from falling over. So when a lot of weight, like cars, people or objects, is put on a compression member, it squishes down a little bit, but it doesn't break.
Compression members are very important and need to be made of strong materials, like steel, so they can hold a lot of weight and keep the structure safe.