I closed the onboarding wizard halfway. How do I reopen it?

The path is Settings → System and about → Getting started guide.

The wizard walks through everything again: interface language and theme, "what do you want to use Fushi for" (tick the library pages and features you need), then — depending on what you ticked — the recommended pack or your own dictionaries, Anki, online services, backup, interconnect, the browser extension and fonts, and finally a guided first tap-to-look-up and your first card. Anything you have already set up can simply be skipped.

Library pages you leave unticked don't appear in the navigation bar; you can bring them back later under Settings → Appearance and interaction → Feature modules.