I'm a beginner.
When I attempt to put a material on a duplicated mesh, the material only applies to the deselected mesh, including the original mesh that was duplicated, and changes freely as my selection changes.
I cannot for the life of me unlink the duplicated object from the original object. When I try to go into object mode it selects the original + the duplicated mesh, and attempting to deselect one deselects both of them, so I can't use Object > Make Single User.