So, here's a link to the kiwix site: https://get.kiwix.org/en/solutions/applications/kiwix-server/ -- I run their server software from my NAS, but you can run it anywhere really.

Go to a browser (MS Edge always refuses to load my Kiwix site, I use firefox) and just type in the IP of the machine you started the server on, plus the port. something like 192.168.1.XXX:80 or localhost:80 if you did it that way.

Then, to download the actual ZIM files, which is the archive format chosen by kiwix (idk why) you can go here: https://browse.library.kiwix.org/

I should note that the zims only load when the server is started, you can't just add new ones while the service is running, you'll need to stop it and restart.

Hope this helps! Message me if you need more info :)