Hi, I,m very new to houdini, I'm pretty much interested on scattering meshes. I want to start to scatter spheres on a “minecraft” shape, I joined a couple of images of what I would like to manage to do before to go with more complex objects to scatter. Anyone have some advices ? I watched a couple of tutorials, I tried with some volume scatter but It's not to be accurate for the shapes, then the copy node but It scatters on points or faces, not on the middle of the cube .Any idea ?

I believe the droid you are looking for is the Points From Volume SOP.

1) Create a volume from your base shape with an Iso Offset.
2) Plug that into Points From Volume and select a Point Configuration (grid or tetrahedronal)
3) Pipe into point source on a Copy To Points SOP.