A 3D printer is a computer controlled machine that builds objects layer by layer. Think of each layer as a two-dimensional cross-section of the final object. By stacking these layers on top of each other, we create a 3D shape. When these layers are very thin, they become almost invisible and the printed object appears smooth and seamless. 3D printing can create highly complex designs, including intricate forms with fine details and interlocking, movable parts.