How 3D printing works is a process that ultimately result in printing directly from a digital file. This process starts with using the computer to virtually design the object that you would like to create.
This is a virtual design that is made in the Computer Aided Design, which is abbreviated CAD file, with a program model that support 3D. This is useful for creating a completely new object, or even using a 3D scanner to copy an object that already exists. The scanner will digitally make the 3D copy of an objects, and then puts it into a program that supports 3D model.
It is possible to prepare the digital file that is created in a 3D model program, which will be printed, then the software will slice final model into either hundreds or thousands of different layers that are in horizontal form. The file is uploaded in the 3D printer, after it has been prepared, which ultimately leads to creating the object one layer after the other.
A 3D printer always reads every slice (or even a 2D image), which proceeds to create that object after it has blended every layer together without any sign being visible on the layer, which ultimately results in an object in three dimensions.