Network Setup

Don’t let the subdirectory / subdomain jargon confuse you too much. That all pretty much went out the window with domain mapping except subdomains is a good way to go if you plan on having others use your multisite as a host. Makes it almost a no brainer to let users create their own accounts.

I think the documentation you’re looking at is pretty dated… what you see in that network setup pane is what you need to do to finish the setup now.

The one thing I would recommend is to do a root install or else follow these instructions to make your WordPress run as if it was a root install… you need to do this before finishing up the network setup.

https://codex.wordpress.org/Giving_WordPress_Its_Own_Directory.

Here’s some better instructions on the Network Setup itself https://codex.wordpress.org/Create_A_Network.

Before you make the final decision to go with a Network (multisite install) this might be worth reading. https://codex.wordpress.org/Before_You_Create_A_Network.

This document might clarify some things also
https://codex.wordpress.org/Multisite_Network_Administration.

And don’t forget to create backups. I use upDraftPlus but it’s a premium plugin for Multisite. I think there’s a few that work well for the Network itself and the individual sites.

Hope this helps.