AND - use this when ALL the words must be in your results. This will narrow your results. Example: apples AND oranges; peanut butter AND jelly
OR - use this to connect synonyms, when ANY can come back in your results. This will broaden a search. Example: women OR woman OR girl; cat OR kitty OR kitten
NOT - use with caution since this will eliminate results with the specified word.
(From Merriam Webster Online.)
Explore the links below to learn more about Plagiarism and how to avoid it.