The Boolean operators (and, or, but not) help you define the relationship between the words or phrases in your search:
|cats and dogs||You get only the titles that mention both cats and dogs.|
|cats or dogs||You get all titles that mention cats, dogs, or both.|
|cats but not dogs||You get only the titles about cats that do not mention dogs.|
Keep in mind that or will expand your search. Don't use or when you mean but not.
Example: You want to find a non-fiction book by Isaac Asimov that isn't about science. If you search for asimov, isaac but not fiction or science, your results won't include "fiction" but will include "science." The search order should be asimov, isaac but not fiction but not science.