Here's a basic research approach and sources to consider while finding secondary sources. Think of these sources as pieces of evidence that will supplement primary sources and assertions that you make.
1. Explore topic context & primary sources (news or non-library sources)
2. Learn the background (WorldCat Discovery: books)
3. Discover scholarly conversations (library databases: journal articles)
4. Support your argument (source citation)
5. Rinse, repeat; drafts & revisions (research librarians, writing center)