Index
An index can be added to your book by clicking the Insert dropdown and choosing index.
AI Index Builder
If your book contains no index entries, you will see an option to build your index using artificial intelligence:

Click on the Build Index button. It may take some time to analyze your whole book and add index entries.

You can modify the index entry by modifying the text box. Use the italics icon: to toggle whether an entry should appear italicized or not. Use the remove button
to remove an entry from throughout the book. The expand button
allows you to see all of the places in the book where the index entry appears.

Once the entry has expanded, there will be a list of all the places in the book that the index is associated with. The checkbox can be used to enable or disable particular entries. To classify the entries into subentries, enter text into the dropdown.
Add an Index Entry

New index entries can be added by using the Add Entry box at the bottom of the screen. Just type in the text for the entry and click the add button: . Inkwell will automatically go through the book and add matching entries to your index. If you want to fine-tune the matches, expand the entries and deselect the entries that you want.
You can combine two index entries by dragging one onto the other.
You can clear the index entirely by clicking on the clear index button: