Combine keywords with AND to narrow your search.
Beethoven AND sonata
Combine keywords with OR to broaden your search. This works well for synonyms.
Moonlight Sonata OR Sonata No. 14
Put quotes around multiword searches to find only documents that contain those words as a phrase.
"Moonlight Sonata"
* (wildcard)
Use a * with the stem of a word to search for all forms of that word.
sonat* searches for sonatas, sonatinas, sonaten, etc.