You can do this on the "About" page for the book, which is in the book's "Settings" section:
You can get to this page by going here:
https://leanpub.com/YOUR_BOOK/settings/about
...making sure to replace YOUR_BOOK with your book's unique web address.
You can also find the "About" page on your book's "Overview" page.
On that page, you will see a section where you can enter your Table of Contents as HTML:
Currently, you'll need to know HTML to use this feature. If you've set up a Table of Contents in HTML and you'd like to share your code with other Leanpub authors who don't really know any HTML, please post about it on the Leanpub Authors Forum!
If you have any feedback or questions about this article, please email the Leanpub team about it at hello@leanpub.com!
If you have any questions or thoughts on writing and self-publishing with Leanpub, please join our global community of authors in our Authors Forum here!
Are you interested in self-publishing, and creating your first Leanpub book? Here are some quick tutorials for our most popular writing modes: http://help.leanpub.com/en/articles/3088382-quick-walkthroughs-for-getting-started-on-a-leanpub-book
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