This may seem obvious but it needs to be documented so I can refer back to it later.
The way you copy a file from folder to another folder on Apple Mac OS/X in the finder is to hold down the option key while dragging the file.
It is hard to find documentation on something this simple – so I am providing this blog entry as a public service and as a personal reminder to save me a minute or so re-deriving it.
Funny how this is so much simpler in the Terminal program where you type “cp ” and then drag the file into the terminal window then type ” .” and enter. :)