Playground is a sample site: a book club with a bookshop, a blog, a contact form and the documentation, all built from blocks inside one layout and styled by one theme. The members, books, events and orders are all made up.
The docs pages are nested under Docs — hover it in the menu, or open the menu on a phone — and the menu itself lives under Site parts → Menus. Everything here is meant to be edited or replaced.