A kaleidoscope is made from two or more reflective surfaces placed at an angle to each other (usually in a triangle or V shape).
These reflectors are surrounded by a tube. At one end of the tube is a collection of brightly colored objects, held in place by a circle of glass or plastic. And at the other end there is an eyehole.
As you look through the eyehole and rotate the tube, the objects at the end of the kaleidoscope move and create different patterns. The reflectors make this into a beautiful repeated pattern that never looks quite the same twice.