The first step in 3D printing something is to make it on a computer. People do this with CAD (Computer Aided Design) software or a 3D scanner. To design models in CAD, people start with basic shapes, and build from that point. 3D scanners are machines that take lots of measurements of the object and automatically make a model on the computer. They can be very fast, but are also more expensive.CAD models are usually saved on computers as STL files. They are saved as lots of triangles, which saves space on the computer.