Some examples:
Tom Jerry	Find documents containing either "Tom", "Jerry" or both, anywhere in the document
Tom or Jerry	Same as above
"Tom Jerry"	Find any document containing "Tom Jerry", as a sentence
Tom and Jerry	Find any document containing both "Tom" and "Jerry", anywhere in the text
(Tom and Jerry) and not dog	Documents containing both Tom and Jerry anywhere in the text, but excluding the word "dog"
Tom near Jerry	Documents containing Tom and followed by Jerry in the next 4 words or so
Tom*	Documents containing words starting with Tom.
sing**	Documents containing variations of the word, eg: sing, sang, sung...