Kiln furniture is kind of like a special set of dishes that can handle being baked in a really hot oven called a kiln. You know how you have plates and bowls for eating your cereal and dinner, but those wouldn't do well in the oven because they might break or melt? Well, kiln furniture is made from special materials like ceramics, refractory metals, or even just plain old sand that can handle really high temperatures without breaking or melting.
The job of the kiln furniture is to hold the things you want to bake or fire in the kiln. So let's say you're a potter and you've made some clay cups that you want to turn into ceramic cups. You can't just put them directly on the floor of the kiln because they might get stuck or damaged. So instead, you put them on little shelves made from kiln furniture. These shelves are called "kiln shelves" and they're usually made from ceramic or a special type of refractory material that won't stick to your cups when they get really hot.
Kiln furniture comes in all sorts of shapes and sizes. You can get round shelves, square shelves, triangle shelves, big ones, little ones, and everything in between. Some special pieces of kiln furniture are even shaped like molds or forms that help you make specific shapes or textures on your clay pieces.
So there you have it, kiln furniture is basically a set of special dishes for baking things in a kiln. They're made from special materials so they don't break or melt in the really hot temperatures, and their job is to hold whatever you're baking so it doesn't get damaged.