I have imported the existing manuscript, but I don’t know how to divide it into 3 parts, with individual chapters. Can’t figure out how to work with the existing text.
Try breaking the manuscript into separate files for each part first. Then, create a new document for each part and copy the chapters into them.
Documents → Split is your friend.
Also, 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 Scrivener’s fundamental operations.
This is doing it the hard way.
Agree document split is your friend but before splitting why not use toolbar to add folders. Name first folders part 1,2,3. Then add more folders and name them chapters1 etc and drag a bunch into each part. Now start at beginning of text and type header chapter one when split add drag into part 1 and the inside chapter one and move on and repeat and next split goes into chapter 2 etc
Assuming your long document Z is in Draft, find where you want Part 2 to start and press Ctrl+Shift+K to split it.
Move to where you want Part 3 to start in the split document, press Ctrl+Shift+K to do a further split.
You now have 3 parts, which you can name accordingly.
Splitting into chapters, go to where you want chapter 1 to start and do a split there.
Keep doing this till all your chapters are split from their part documents and from one another and shift the chapters in your parts hierarchically to the right of the parts.
But as was advised read the Interactive Tutorial so you have an idea why you’re doing this.