Using Boolean operators in a database is highly recommended, as this approach usually generates the most useful results. Databases are not "intuitive" like search engines (e.g., Google) - they must be "told" how to process a search query. Boolean operators let you "tell" the database what you want to see in your results.
Use AND to connect KEYWORDS - Retrieves sources with both/all terms [refines search]
Example: diabetes AND adult AND self-management
Use OR to connect SYNONYMS & LIKE CONCEPTS - Retrieves sources with either/any term(s) [broadens search]
Example: heart attack AND (female OR women) AND symptoms
Use NOT to EXCLUDE word(s) - Eliminates sources with the word(s) following NOT
Example: Omega-3 fatty acids NOT fish oils