The search results are determined by the combination of information entered into the search fields. The more information you enter, the fewer search results will be returned. The search engine will try to match all the words that you enter in the search fields.
When searching it is best to enter 2 or 3 words as your search criteria. If the first search yields too many results, then try entering more search criteria to reduce the search results. Keywords also work well when you want to see all the book available in a genre, such as History, simply enter that word and everything having to do with history will come up. At that time you may want to narrow down your search, such as Medieval History.
Even if you don't know the exact title of the book, enter the words you are certain of. If we have the book it will come up if you added the correct word(s).
ISBN stands for International Standard Book Number, and you will start finding them on books beginning in 1970. It was a ten-digit number in the United States (nine-digits in the U.K. until 1974). They identify the publisher and are uniquely assigned to a particular title. Beginning in 2007 this number was expanded to thirteen digits. The ISBN can normally be found on the back of the book and on the inside page where copyright information is printed. Occasionally there will be a book later than 1970 that does not have an ISBN. These are often private press books with a limited run. Then a title search will work well. This is a very reliable way to search for books because they are generally not assigned to more than one book.