Online indexes of journal articles, abstracts. Other types of databases also exist, including many that contain full-text journal articles. Some databases also contain citations for books, book chapters, newspaper/magazine articles, and more. More info
The words "AND," "OR," and "NOT" can help you make a search more precise.
For example, the search 'films AND psychology NOT children', will return a search with results that contain the keywords 'films' and 'pyschology' but not 'children' - important if you are only looking at adolescent psychology in films.