Encyclopedias are the best place to get authoritative introductory information. The articles are carefully written to give broad understanding, and key terms will often be highlighted and linked to more articles. And, the encyclopedia will give you a citation!
When starting a research project, your first step should be an encyclopedia. You can read Wikipedia, but you can't cite it because the articles are crowd sourced with many different authors. Wikipedia can a good place to find citations to books and articles. Keep in mind that Wikipedia articles are written at a high reading level and may be hard to understand sometimes.