By default the search engine tries to locate pages which have exact matches for all of the words entered in your search query. You also could trie to locate pages which contain any words in your search query. Please select in the option "Any word".
In addition, there are several ways to modify the default search behavior.
* 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*