Smooth voxel terrain with digging(help)

I have done research to find tutorials on about how to make smooth voxel terrains with digging but apparently that thing is nonexistent when it comes to tutorials, only minecraft like terrains. For beginning the terrain can be just a plane but I would like to make it into a planet someday. I also stumbled upon cubiquity, it’s literally the perfect example on what I want to achieve but I don’t understand cubiquitys code so I started doing research and found nothing but normal voxel terrains. Could someone “Atleast” point me in the right direction to achieve something like cubiquity with digging also and someday procedural generation. Thanks!

Do some research on Marching Cubes and 3D Perlin Noise (or using Perlin Noise as a density function).

Go there, read it all. Problem solved.