Boolean operators allow you to combine your keywords into search query that the databases understand. The words AND, OR are the most commonly used Boolean operators. The third is NOT, which is difficult to use because it can exclude useful results.
AND combines your search terms and looks for them together in search result. Example: A search for Hip Hop Music AND Rap Music will retrieve records that have both keywords; Hip Hop Music and Rap Music.
OR separates your search terms, finding records that contain either keyword. Example: A search for Hip Hop Music OR Rap Music will retrieve records that contain just one of the search terms as well as records with both of the search terms.
NOT finds records that only have the first keyword, excluding the second keyword. Example: A search for Rap NOT Country will find only records containing the Rap but not the second keyword. However if there was an article title: Why Rap Music Tells a Better Story Than Country Music, the database will ignore the article even though it is useful because of the use of the Boolean Operator NOT. I do NOT recommend use of this Boolean Operator, it can be too exclusive and hurt your research.
Question: I want to know more about music's influence on Urban Culture?
Your search should be constructed as an using Music AND Urban Culture. Your results will include records where both terms appear.
You can add an additional term to your search such as Los Angeles. Your search will be narrowed down to only have results that have all three words Music AND Urban Culture AND Los Angeles.
Question: I need to find information on Freeways?
Think of synonyms for the word, Freeways OR Highways will help you retrieve more results.
Question: I am look for information on Hybrid Cars?
By NESTING you can use both AND and OR: Hybrid AND (Cars OR vehicles)