Hi,
it’s actually quite simple. In one of the links I posted above they show you how to export an stl-file:
Export["filename.stl", output]
It’s as simple as that. Much of the remainder of the code they use is to make the two dimensional surfaces into three dimensional objects (obviously two dimensional objects cannot be 3D-printed).
One good piece of advice is to additionally use MeshLab to post-process the file and prepare it for printing. It is really quite straight forward.
Cheers,
Marco