At its simplest, a query can be just a word or a phrase. But with the tips on this page, you can expand the focus of your query to give you more complete results. 
Although overriding the default switches can yield better results, changing the defaults usually increases search time.

Operators

 
AND or [space] or &
Used between two words to find files containing both words.
Example: apple & orange
will find files that contain both words. (Note: Multiple search words without intervening operators are connected by an implied AND operator.)
OR or | [vertical bar]
Used between two words to find files containing either word.
Example: apple | orange
will find files that contain either apple or orange.
NOT or ! [exclamation]
Used before a word (or words within parentheses) to find files not containing the word(s).
Example: apple & ! orange
will find files that contain the word apple but not the word orange.
NEAR
Used instead of AND, for words close to each other. For example, both of these queries.
Example: apple and orange and apple near orange, look for the words apple and orange on the same page. But with NEAR, the returned pages are ranked in order of proximity: The closer together the words are, the higher the rank of that page.
.. [two periods]
Used between two words, the ORDER operator finds files containing both words, with the first word occurring before (but not necessarily adjacent to) the second.
Example: apple..orange
will find files that contain both apple and orange, with apple appearing earlier than orange.
" " [quotation marks]
Enclosing words in double quotation marks will find files that contain a PHRASE--a sequence of words in succession.
Example: "apples are red"
will find files that contain the phrase "apples are red".

Operator Precedence

If multiple operators occur, they are evaluated in this order:

  1. NOT
  2. .. [order]
  3. AND
  4. OR

Use parentheses to modify the default evaluation order.

Case and Wildcards

Use the following switches before the word (or a parenthesized group of words) to which they apply.

/NOCASE
Ignore case when matching words. (Default)
/CASE
Respect case when matching words. Case-sensitive searches are more time-consuming.
/WPCASE
Uppercase letters in the search word(s) much match exactly; lowercase letters will match either case.
/WILDCARD
Treat "*" and "?" in search word as wildcards. (Default)
? matches any single character.
* matches zero or more characters.
/NOWILDCARD
Treat "*" and "?" in search word as characters.
/PARTIAL
Equivalent to adding "*" before and after the search word(s). Note: This option increases search time significantly.

Proximity

The following switches take effect when searching for multiple words. Use the following before a parenthesized group of words to which they apply.

/WITHIN=n or /n
Finds only files where the words are within n words of each other.
/SENTENCE
Words must occur in the same sentence to qualify as a match.
/PARAGRAPH
Words must occur in the same paragraph to qualify as a match.
/DOCUMENT
Words must be in the same document. (Default) If present, this switch overrides other proximity switches.