Yes. When you buy your first Leanpub book, we create an account for you so that you can always access the latest version of every book you buy. After your first purchase, we will email you with download links for the book. The download links in the email will always point to the latest version of the book.
The email will also have a link to the Leanpub Library for your new account. Clicking on the link will open your Leanpub 'Dashboard', where you can see all your purchases, set your password and change your account settings.