By default the search engine tries to locate pages which have exact matches for all of the words entered in your search query. If that fails, it then tries to locate pages which contain any words in your search query. If that happens a short message is displayed at the top of the search results indicating this has been done.
In addition, there are several ways to modify the default search behavior.
To match an exact phrase, use single quotes around the phrase
Example: 'free search engine'
If a query word ends with a * all words on a page which start the same way as that query word will match.
You can use the following boolean operators in your search: AND, OR, NOT. These operators MUST be in capital letters.
Example: (contact AND us) OR (about AND us)