Using AND in your search query means your results will show only items that include ALL of your search terms.
Using OR in your search query means your results will show all items that include ANY of your search terms.
Using NOT in your search query means your results will EXCLUDE certain items (e.g., Italy NOT France).
For modern authors, simply search on the name (given name) and surname (family name), e.g., William Shakespeare.
For medieval authors, the Latin form of their names is the standard for searching (e.g., Franciscus, Clara, Bonaventura), though English, Italian and Spanish forms may also produce results (e.g., Francis, Chiara, Buenaventura).