You can expand or narrow your search results by using connectors (or operators) to form a relationship between your search terms.
AND - connects your terms together. You will only retrieve results that contain ALL your terms
OR - expands your results. You will retrieve results that contain ANY of your terms
NOT - excludes terms from your results
More search operators
(brackets OR parentheses) - brackets groups terms together, particularly useful for grouping synonyms in an OR search
"quotation marks" - put terms in double quotation marks to search for the words as an exact phrase
You can use a database or search engine's 'advanced' search options to bring up the AND, OR and NOT connectors, and also to be able to choose which field is being searched for your terms. A regular or 'basic' search will search for your terms across any/all fields, but in an advanced search you can specify to only search fields such as 'title', 'author', 'subject' or 'abstract'.