Boolean operators are words you can use between your search terms to either broaden or limit your search.
Use OR to broaden your search. For example, if you search advertising OR commercials, you will find articles that include either term.
In contrast, use AND and NOT to narrow your search. For example, if you search advertising AND commercials, you will only find articles that include both terms.
And, if you search advertising NOT commercials, you will find articles that include the word advertising, except for those that also include the term commercials. In Google, use a minus sign instead of NOT (e.g. advertising -commercials).
Use a truncation symbol (the asterisk * is the most common) to look for different word endings. You can also use it to replace letters.
You do have to be careful with truncation. Sometimes you might get unexpected results.
Use quotation marks to search for a phrase (two words or more).