The search field at the top of pages finds all terms in the title and author fields.

If you use the search box you may search by author, title or categories.
If you use multiple search terms the resulting matches shall be books that include at least one search term.
If you use both the 'title' and 'author' search boxes you will narrow your search because the resulting books shall contain search terms in both the 'title' and 'author' fields.