Psychologists and students of psychology sometimes need secondary information. Secondary information is information that's a degree separate from the situation in which it was created. So, new research findings, reported by the researchers themselves, is primary information. A document that takes that research, and interprets it for a broad general audience, such as in a popular magazine or news article: that would be an example of secondary information.
Psychologists go to secondary information when they need information that's broader than a single research study. They might need an overview of all the research in an area, or a review of how a concept has evolved, or a biography of a person.
Where can you find secondary information? It is often contained in articles called review articles, and in books.
For review articles, try PsycInfo database. For more details, see the Reviews tab.
To find books, search with the main search box on the library homepage.