To access the library databases, just click on the "databases" button, located below the Primo search box, off of the library homepage. You can search databases by title or subject.
Watch this video to see a demonstration of how to use the advanced search in the database JSTOR.
If you're initially having difficulty locating sources in the library databases, one strategy is to search Google Scholar. Google Scholar can be more forgiving than the databases with search terms. Google Scholar also has features to help you with citation chaining. You can see not only which sources were cited in a specific resource but also which sources went on to cite that particular resource. If you use Google Scholar, it is always a good idea to also consult the library databases to reduce the possibility of bias in your searches.
The video below summarizes some of the search tools in Google Scholar.