A 3D printer is controlled from a Computer-Aided Design, better known by the abbreviation CAD. Using 3D printer software, you can create a CAD model for the object you are going to print. Then the CAD file must be converted to an STL file. For example, the slicer software can send the file to the 3D printer via G code.
Using 3D slicer software you can convert the STL file to a format that is supported by the 3D printer. The slicer software divides the object into layers that are printed. The thinner the layers, the higher the quality of your final 3D print. You also use the slicer software to indicate, for example, whether your design can be hollow or needs to be filled.
With the slicer you cut the STL file into slices, as it were. With this 3D slicer software you can convert the sliced model into G code, the control code for the 3D printer. For more information, see our slicer software page.
On websites such as Thingiverse and MyMiniFactory, you can download ready-made STL files. Ideal for if you don't like to design objects yourself.