How do I tell the AI exactly what a chapter should contain and in what structure?

With the Structure button. Open your book and hover over a chapter in the chapter list — a small "Structure" button appears (a table icon). Click it and write your requirements in plain words: "Compare the 5 tools in a table with columns price, best for, limitations; end with a bulleted action checklist." Save, then generate — or regenerate — that chapter. The instructions are binding: the AI presents exactly that information in exactly that structure. This also works on existing chapters: set the structure, press the chapter's regenerate button, and the chapter is rewritten to spec.