What is the "Automation" button in Excel's Add-In dialog box? What
does it do? What is it good for and how does it differ or relate to
"Add-Ins?" I would like to use/try it (to improve my Excel skills),
but I find no documentation as how to use it.

The only thing I find in the help documentation from Excel is: "You
can click the Automation button to list all Component Object Model
(COM) add-ins available to load into Excel."

Wow. That doesn't help.

Any knowledgable direction would be much appreciated...