To find more databases check the Research Guides from other disciplines relevant to your topic.
Boolean Operators are short words used to combine search terms in logical operations. Most databases, discovery layers and search engines recognize them and use them to to bring search results that fulfill the requested operations.The most common are AND, OR and NOT. They are written in capitals to differentiate them from regular keywords.
Check the image below to understand how each of them affects the results of your searches. Parenthesis are used to combine different sets of instructions and to signal the order in which they should happen.