Styrofoam is a material that feels kind of like a squishy marshmallow, but it's usually shaped like a cup, a plate, or a big block. It's a type of plastic made from something called polystyrene, which is a special substance that can be molded into all sorts of different shapes and sizes.
When it's made, a bunch of tiny beads of polystyrene are squished together and heated up until they melt and become sticky. Then, they're poured into special molds that shape them into whatever shape is needed. Once it cools down and hardens, the result is a piece of styrofoam that is light, durable, and great at keeping things warm or cold.
Styrofoam is very useful for things like cups and plates, which can be disposable so people don't have to worry about washing them. It's also often used to package fragile things like electronics or dishes so they don't break during shipping. However, styrofoam isn't great for the environment because it doesn't break down easily like some other materials. That means it can sit in landfills for a really long time, which isn't good for the planet.