Databases use controlled vocabulary to index or tag articles and books. Successful searching is dependent on discovering what those words (terms) are.
Some databases have tools to help you find the controlled vocabulary terms. These terms usually include definitions. For example -->
Take your topic and look for key concepts. Take those concepts and brainstorm related terms.
1) Identify a question or topic
2) Look for key concepts
What is the significance of male protagonists who are presented as social outcasts in young adult fiction?
male OR man OR boy
social outcasts OR misfits OR nerds
young adult fiction OR YA OR teen
Use quotation marks to search for a phrase
Use a symbol (* is the most common) to look for variant endings of a word