The shown code generates the volume from an implicit function (the sphere). There is also no texture, no material information and no elaborate lighting involved, so what’s shown will not be spectacular…
the examples only work by loading predefined shapes
The typical use case is to show a dataset that was acquired by some imaging technique like computed tomography etc; but for test purposes it’s not practical to include a larger dataset, hence the generated sphere volume.
and I need to know how to set individual points.
I’m still a bit unclear on what exact positions you want to put your data? See e.g. the Paraview docs for an overview on the different grid types that vtk supports - the simplest case, for which vtkImageData is suited, is a " Uniform rectilinear grid (image data)". What kind of data do you want to show exactly? Maybe you have it in some file format that vtk can load already (e.g. dicom, raw file, etc.). Maybe you don’t need to “set individual points” by yourself?