In this lesson on design and technology, the focus is on 3D printing, an additive manufacturing process primarily used for prototyping. Students learn that 3D printing involves designing digital models using Computer-Aided Design (CAD) software, saving them as STL files, and using a program to slice these files for the 3D printer, which constructs the object layer by layer using a filament. This contrasts with subtractive manufacturing, where material is removed from a block to create the final product, often resulting in more waste.