The AND operator narrows your search. Ordering "a burger and fries" gets you both, so using AND between keywords returns results with both or all of your keywords.
The OR operator expands your search. Ordering "a Pepsi(TM) or a Coke(TM)" gets you a brown soda with cola flavoring, so using OR returns results with either of your keywords.
The NOT operator excludes something from your search. Ordering a beer but NOT wine will get you a beer. So use NOT to exclude words you don't want to find. For example, you want to search for articles about football but NOT college football.
Search statements include keywords and the logical, or Boolean operators that connect them. To create a search statement, combine your keywords with AND, OR, and sometimes with NOT to strategically look for your information.