When looking for articles, start in some of the bigger bibliographic databases such as Pubmed, CINAHL, or Cochrane Library. You'll notice the phrase "Scholarly literature" or "scholarly journal" from time to time, and all it really means is that an article was written by an expert in a field and then reviewed by their other expert peers before being published (hence the term "peer review."). It's not a perfect system, but it's considered higher quality and more unbiased than a letter to an editor, a magazine article, etc. Use this short list of resources, but also check out the "More Resources & Tools" page for more resources.
Remember, you need three articles at minimum, so ask your librarian if you get stuck and need help.