How do I leave the index out of an export, or move it?

Open the book and look at the Export card on the right, under "Include in book". Once your book has an index, "Index" is a row in that list. Untick it to leave it out of the export. To move it, drag its row or use the arrows; by default it is the last section of the book, after About the Author, which is where a printed book has it. The "Edit" button on that row opens the Index page. From version 1.9.15.