Is there a step by step tutorial on Fire 8 and Calibre?

[Blue2u]

ETA: I've decided to return it, so no reply is necessary, thank you.

I've searched the forums and can only find older posts on basic setup. I just got a Fire HD 8 and I am completely at a loss as where to start.
I've used Calibre for years with various versions of Kindle Paperwhite to sideload all my purchases and sync via USB [my preferred method].

I'm quite tech-challenged. All my books are in AZW3 format. I was able to add some [even after an error in Calibre] onto my Fire, but where do they go? Some older posts suggest MOBI format? Do I need to change mine to MOBI?
How do I read them? What folder should they be in?

Sorry, I'm just lost and basically am looking for a very basic, talk-to-me-like-I'm-a-toddler walk-through.

I basically wanted to try the Fire as a cheaper alternative to KPW but I have a feeling that maybe was a mistake.

And I read a few posts about people getting errors with Calibre/Fire8 but like I said, it did let me add books...

The error I got in Calibre [even though it did let me add books]:

calibre, version 6.24.0
ERROR: Unhandled exception: <b>WPDError</b>:C:\r\src\src\calibre\devices\mtp\windows\conten t_enumeration.cpp:337:Failed to EnumObjects() of folder from device:[hr=0x80042009 wCode=7689] IDispatch error #7689: o16

calibre 6.24 embedded-python: True
Windows-10-10.0.19045-SP0 Windows ('64bit', 'WindowsPE')
('Windows', '10', '10.0.19045')
Python 3.10.1
Windows: ('10', '10.0.19045', 'SP0', 'Multiprocessor Free')
Interface language: None
Successfully initialized third party plugins: Gather KFX-ZIP (from KFX Input) (2, 5, 0) && DeDRM (7, 1, 0) && Package KFX (from KFX Input) (2, 5, 0) && Author Book Count (2, 2, 3) && Count Pages (1, 13, 4) && EpubMerge (2, 16, 0) && EpubSplit (3, 6, 0) && Find Duplicates (1, 10, 8) && KFX metadata reader (from KFX Input) (2, 5, 0) && KFX Input (2, 5, 0) && Set KFX metadata (from KFX Output) (2, 3, 1) && KFX Output (2, 3, 1) && KindleUnpack - The Plugin (0, 83, 1) && Modify ePub (1, 8, 2) && Obok DeDRM (3, 1, 1) && Quality Check (1, 13, 6)
wpd.WPDError: C:\r\src\src\calibre\devices\mtp\windows\content_e numeration.cpp:337:Failed to EnumObjects() of folder from device:[hr=0x80042009 wCode=7689] IDispatch error #7689: o16