It's basically just like Google, except the search results are all books.
Just do a search on the Google Print homepage. When we find a book whose content contains a match for your search terms, we'll link to it in your search results. Click a book title and you'll see the page of the book that has your search terms, along with other information about the book and "Buy this Book" links to online bookstores (you can view the entirety of public domain books or, for books under copyright, just a few pages or in some cases, only the title’s bibliographic data and brief snippets). You can also search for more information within that specific book and find nearby libraries that have it.A quick test shows it to be strangely skewed to academic texts. A search on "Money by Martin Amis", for example, doesn't appear to find the novel itself at all.