...and I <shrug> totally agree with his assessment. I went from my D5 to the Z9 *almost* without a hiccup, mostly because I was very familiar with Nikon's menu system. In fact, all my upgrades since buying my D70s in '06, have been fairly easy because of said familiarity. Sure, there were aspects of each upgrade that needed to be mastered and me, being in the same place as our
OP, never really got into the esoteric nature of Nikon's literature. We all learn differently and I gravitate to trusted sources that have served me well for years...most of them on YouTube. Visual learners in general approach getting a working knowledge of something this way...through *seeing* how it's done, or really good written tracts that lay it out in an understandable manner. This is nothing against those who choose to dig in to the manual, not at all, but only to bring it forward that there are other ways of doing things. The Z9 to me was initially difficult to set up, so I found both Steve Perry and Hudson Henry to be super helpful...but I was out shooting with it hours after unpacking it, because I *could*! I'm now very intuitive operating the camera, but even so, with firmware updates and such, I tend to watch alot of vids...some not so helpful, some with a nugget or two, and some just badass. So, to each his or her own...and shoot 'til you can't do it anymore!

If I was the owner of a Z8 my first step in learning the camera would be to download the Nikon guide for it. If a wildlife or action photographer there is no way I will miss Steve Perry's instructions on how to use the Nikon AF.
Rick is right, there are very good books available to learn the Z8 but that means extra money you have to pay. YouTube has plenty of videos from well known photographers talking about the camera. Google also offers lots of information.

In my case I never needed to buy a book to learn a camera I owned. The guide supplied by the manufacturer and my use of videos in YouTube have always been enough but that is me.

As far as a third party "book", Steve Perry who is a frequent contributor here has his own website (https://backcountrygallery.com/) and is a well known independent Nikon/Canon tester, has a number of online "BOOKS" about the Z8 with settings specific to it for various things.
As far as your other questions, ...without trying to be a Smart A, or being a Smart A, pull up a web browser & submit your own questions....all of the information is out there & you will retain the answers learning something

Unless you are completely unfamiliar with cameras, particularly in the Nikon environment, I would suggest that the operation of the Z8 isn’t really all that different from the Nikon Dslr’s. I found it pretty easy to step up from my Nikon dslr’s to my Z8, except (a BIG except) for the incredible (and incredibly different) auto focus capabilities. To begin to understand what the Z8 can do AF wise, I found Steve Perry’s ebook devoted solely to the AF function work every penny.

https://bcgwebstore.com/product/secrets-to-the-nikon-autofocus-system-mirrorless-edition/

Can’t recommend it enough. If you are not familiar with general use of Nikon bodies, you may need a more general primer, but you may still want that AF book to understand the intricacies of the 8’s amazing capabilities. I am intimately aware of basic Nikon camera design, but found figuring out how to max out the numerous AF variations to be impossible without the help.

BTW - ignore the suggestion about the free Nikon guide. It’s as useless as tits on a bull.