When you set up a new book on Leanpub, you will be asked to enter a URL:

This is the web address for the landing page on Leanpub where people will be able to buy your book.

We suggest short URLs that reflect the title of your book.

For example, if you were creating a book with the title "Space Robots", you might choose the URL "spacerobots":

If you have a longer title, like "Introduction to Space Robots", you might want to try something like "intro-space-robots":

You can change your book's URL any time. Here are the instructions:

http://help.leanpub.com/en/articles/478705-how-do-i-change-the-url-for-my-book

That's it!