Windows computer registered as a device

My Windows 10 computer used to be registered as a device (it's authorized too by the way). Frankly don't know how it got registered in the first place. What does it even mean? Is it "registered" with iCloud or something? Anyway, I made the mistake .. I think .. of cleaning up my device registrations in my Apple account. Found two that were associated with my Windows computer .. and .. like an idiot deleted them both (didn't touch my iPad or iPhone). Actually thought this was the same as authorization .. which clearly it's not. So .. have these questions:

1 - what is the distinction between a registering a computer as a device and authorizing it?

2 - what is the impact of of having a computer using iTunes that is authorized as a computer but not registered as a device?

3 - if not being registered as device impacts what I can do from iTunes, how do I restore -- or "re-register" my computer as a device?

4 - This all came about because my iTunes in Win10 decided to take a hike into la-la land (refused to read the contents of my mobile devices correctly, wouldn't sync, wouldn't back up). After a huge effort -- I managed to successfully completely uninstall and reinstall iTunes so that the 'wonky" behavior it started having last week was history. My iPhone is now happily syncing to my iTunes. And I'm in the process as I write this .. of achieving the same with my iPad Mini (my old iPod Classic is next). It was during the uninstall effort that I made the perhaps unfortunate decision to "clean up" my registered device account.

Any advice folks can offer me on this would be most appreciated.

Ha! Ha! I just noticed that this community help seems to know about my Windows computer .. asked me what device I'm talking about .. and listed my Windows computer called Alexander .. as a choice. So now I'm really confused! How could this community help area know about Alexander???