Scholarly journals undergo a process of peer-review. Because these journals are written by experts for other experts (and those who hope to become experts - like you!), in this case the "peers" would be other experts in the discipline. The peer review process is rigorous, and helps to ensure that the authors' methodology is sound and the article contributes meaningful new information to the field. Scholarly journals and articles are sometimes referred to simply as "peer-reviewed."
In ONESearch, you can use the Refine Results tools to help you limit your results in a variety of ways. Click the Peer-Reviewed Journals filter (listed under Availability) to limit your results to scholarly articles.
You must find at least four scholarly sources for your research paper, including two scholarly digital sources. Books from the library will usually be scholarly (but you can check with your professor or a librarian if you're not sure). The NC State University Libraries has an excellent interactive visual that identifies the key features of a scholarly article. For a refresher on identifying whether an article is scholarly or not, please view the video below.