Ok... so here are the steps I've taken to thoroughly screw up my computer (thank God created system image just before this

)
1.Clicked Switch/Create; selected 'Use previously existing library at new location' and the location was '.../Calibre Library' (the bad default).
Result: My books disappeared from Calibre... so ok (brief panic attack before logic set in

).
Next:
-Although you (
theducks) didn't say it, I figured I need to switch back to Calibre-Library since I technically can't rename current one (right?). So I did a 'quick switch' back. And then I could 'see' the original 'Calibre Library' under my C:/../Calibre-Library. I was able to rename it to 'Junk Library'.
-I then 'quick switched' to Junk Library, and renamed 'Calibre-Library'.... incorrectly of course. I didn't realize that I should delete the C:/../ before the folder name so (I think) I inadvertently created another library (_UserName_Documents_Calibre Library).
-So I again attempted to rename Calibre-Library by deleting the C:/../ .. and this time it worked.
- 'Quick switched' back to the newly named 'Calibre Library' and my books showed up so I knew it was the proper folder.
- Was now able to delete (better term: disconnect) the Junk Library from Calibre (note: actual folder needs to be deleted manually), deleted the accidentally created library '_UserName_Documents_Calibre Library' which evidently did not have a folder associated with it.
Everything
looks good.
Lessons I think I learned:
1. A 'library' in Calibre is not a 'folder' in Explorer; rather it is
associated or
linked to a folder in Explorer. That is why it does not immediately show up in options. It is not an equivalent of 'browse your files'.
2. You may need to use Switch/create command to establish that link so that you can view that folder within the Calibre options. (This is why I could not 'see' the two libraries initially and switch between them.)
3. Further to 'Switch' not being an equivalent to 'browse for folders', you have to be prepared to
manually enter the full directory of the folder in order to establish the link.
4. Renaming refers to the folder only. So if the directory link is showing as a default, delete all but the actual folder name.
5. Creating a library does not mean creating a folder on your system... (I haven't checked this but I am assuming it). It refers to the creation of a link to a folder. Therefore, when you 'delete' a library, it does not delete the folder, it simply severs & deletes the link allowing you to delete the folder manually. Conversely, if you want to create a library, you must create the folder manually to establish the link.
Sooooo... THAT is the thought process that allowed me to get it done.

I know it is technically over-simplified, but I do not think the inaccuracies are relevant at this level.
I believe my main problem was some basic preconceptions in how Calibre works - primarily that folders & Libraries were the same thing... and that is not quite so. But this was causing a lot of confusion for me. I hope this detailed breakdown helps someone else who may be equally confused (please ... don't let me be the only one!
Thanks so much to @theducks and @BetterRed for patiently humouring me.
Saints. The both of you.
(Sorry about some of the grammatical issues.. I was typing while I was doing it - so some of my tenses may seem off. )