If you enter mulitple words, a search is done for content containing all of the words. If you want to search for any of the words entered you can use the OR operator (note that OR must be in ALL CAPS).
For example: road OR highway
You can also use wildcard searches, using ? (single character) or * (multi-character).
For example: te?t will return "text" or "test", while de*t will return "dent", "debit", or "decent"
Also you can use + to indicate that the word must appear in the results or - to indicate a word must not appear in results.