How to Copy Files from PC to MyCloud Mirror

I am trying to learn about the pros and cons of using a NAS and so am experimenting with a WD Mycloud Mirror.
My problem is that I cannot copy files from my Windows 10 PC to the NAS if the share is not in the Public share.
So I create a share, and to keep things simple, mark it as Public (strangely the share is not created in the Public Share).
! See my created share NasStokesShared in this image.
nas shares|205x158
Using Windows File Explorer I can drag files from the PC to the default Public shares (a pop up message says ‘copy files to xxx’). But if I try to drag a file to a share outside of the Public share a red cross is displayed and the file is not copied.
If I try the ‘copy an paste’ route then when I right-click on the NAS share I dont get a ‘paste’ option.
This seems so basic; what am I missing?

From OP: bit more information. I cannot drag files from the PC to route shares such as ‘Public’ or my own ‘NasStokesShared’, but I can drag files to any sub share of these.
I can, using Windows File Explorer create sub shares in NasStokesShared