Reference
Reference is where you look up specifics. Authoring pages teach how to use a surface, Concepts pages explain the mental model, and Reference tells you what a particular function does, what fields a particular event has, or which category a menu command lives under. Search often lands here.
Glossary defines every capitalized term used elsewhere in the manual, with a link to the page that teaches the concept in full. Start here when a word in another page is doing a lot of work you do not recognize.
Menu and shortcuts lists every editor command and its keyboard shortcut, grouped by menu.
Project Settings documents each field in the project-wide settings dialog.
ICU format explains the placeholder syntax used by the localization system.
Entities is the catalog of the data model’s building blocks. Every entity kind (scene, character, activity, and the rest) gets a page describing the fields it carries.
Event types is the parallel catalog for events. Every kind of event (enter scene, set variable, skill check) gets a page of its fields and behavior.
Expression operators covers the small set of Boolean and arithmetic building blocks that show up in every condition.
Expression functions is the fifty-plus-page catalog of the runtime’s expression library. Look here when you know the shape of the value you want but not which function returns it.