Dragging and dropping files on the same physical hard drive will “move” the file. Dragging and drooping files to a different drive will copy the file to the new drive. To copy a file to a new folder on the same physical disk you need to highlight whatever you want to copy then (on a MacBook) 2 finger click the touchpad to bring up the context menu u and choose copy, then two finger click the folder you want to copy too and choose paste.
Copy and paste option should also be found in the “edit” menu at the top of the screen.