Use OR to combine synonyms for your search terms. Many databases have a thesaurus where you can look up related search terms. You can also use an online thesaurus like the Merriam Webster Thesaurus.
Example: [ USA OR America OR "United States of America" ]
Use quotation marks to search for exact phrases.
For example, if you type [ cost accounting ] in the search bar, the database will return results that include the terms "cost" and "accounting" anywhere in the articles. However, if you type [ "cost accounting" ] in the search bar, the database will only return articles where the two terms appear directly next to each other.
Be careful though - if you have too many words in a phrase, you may not be able to find enough resources. Only use quotation marks around established phrases in your field of research.