You'll finish with: You know when to reach for it.
Design is the canvas surface — you describe what you want, it builds it, and you push it around by talking rather than dragging.
It is not a replacement for a designer on anything that defines your brand. It's for the fifty documents a year that currently look like a Word file because you didn't have time.
What it's for, and what it isn't
First drafts look generic. Not bad — generic. That's not a flaw you prompt your way out of in one go; it's the starting point you push away from, which is what the next chapters are about.
If the output is something a person looks at, it's Design. If it's something a person reads and then does, it's a document — write it in chat.
If you can't find Design at all, that isn't you doing it wrong. It is in beta on Pro, Max, Team and Enterprise, and on Enterprise it is switched off until an admin turns it on. That is an account setting — no amount of hunting through the menus will produce it.