1) You start with a CAD program and design what you want.
Here is an example; in TinkerCAD we have created a miniature replica of an old Nintendo Game Boy. We can save this as an STL file, which is one of the standard file types for 3D designs.
2) We drop the STL file into a Slicing program, in this case, Slic3r.
Slic3r converts your STL into a file that can be read by the 3D Printer. It slices the file into small layers that you can set (.15mm is the standard), so the printer will know exactly where to print on each level. We then export it as a G-Code to a MicroSD card.
3) Time to Print!
Once the card is inserted into the printer, we select the file and begin the printing process. Prints can take any amount of time, from very small prints done in a few minutes to complex prints that could last 24 hours or more. In this case, the print will only take 45 minutes.