I’m sure this an FAQ, but I can’t find a clue to get started. I’ve not played with Compile yet, so I was hoping to figure out “the correct” way to add Parts structure to the book before having to figure out Compile.
Thoughts? Can I get a link or pointer? 
You can create as many folders under the Draft folder as you like, and define them as Parts, Chapters, or whatever. You want the Project -> New Folder command, or the dropdown next to the ‘+’ icon in the toolbar.
If you haven’t already, I’d recommend taking a look at our Interactive Tutorial, available from the Help menu. It’s a good overview of fundamental operations like this.
Katherine
You could argue that almost the whole point of Scrivener is that it allows you to mess about with the structure of your writing very easily. So don’t fall into the trap of thinking that you need to set up the structure before you start. It is better to start and allow the structure to emerge as you work.
Any item in the Draft/Manuscript part of the Binder can hold text.
Any item can likewise have the folder or document icon, or any other icon, irrespective of it containing text or not. (the difference between folders and documents is basically only the icon)
Any item can also have sub-items, and those sub-items can also hold text (or not) and have any icon, and have their own sub-items.
How do you want to organize your text while writing?
Section Types have a feature in the project settings that allow them to be assigned by the structure of your binder. You can decide what that structure is at any time (automatically determined Section Types can be changed globally with the settings in Project->Project Settings).
So, you could put parts folders in the draft folder, and within each part folder, you could put chapter documents. Or instead of chapter documents, you could create folders for each chapter, and put one or more “scene” documents within those folders. Then you can tell Scrivener what the default section types are based on your chosen hierarchy, and from there, you can run the compile process, and assign section layouts (how document titles, body text are formatted) to each of the section types you’re using.
In my opinion, you should start writing, and determine how you want to distinguish your parts and your chapters from one another. Later, you can fiddle with the auto-assignment (and possibly occasionally manual assignement) of section types and how they’re formatted during compile.
All, thanks! Terrific.