By default, the search engine tries to locate pages which have exact matches for all 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 behaviour.

1. + and - qualifiers
   If you prefix a word with + that word is required to be on the page.
   If you prefix a word with - that word is required to not be on the page.
     Example: +always -never
    
2. * wildcard
   If a query word ends with a * all words on a page which start the same way as that query word will match.
   Example: gift*
    
3. ? wildcard
   If a query word contains a ? any character will match that position.
   Example: b?g