Once you install the app, you need to find out the Google “book code” for the book you want to download. To determine the “book code”, look at the URL in the address when you are looking at the book in Google.

For example:

http://books.google.com/books?id=bU8EAAAAMBAJ&printsec=frontcover&source=gbs_hp#v=onepage&q=&f=false

The “book code” is the value in the id variable (The string from “id=” to the next “&”).
In the above example, the “book code” is bU8EAAAAMBAJ.

Use the book code to start downloading books using Google Book Downloader.