Your professor expects you to use the scientific or peer-reviewed journal literature to support the ideas presented in your seminar. Here's a quick overview of how to identify these journal articles.
If the article is NOT written by the person or group who did the research, it is NOT a peer-reviewed or scientific article. Don't be misled by journal titles like Scientific American or Bioscience. They are great magazines but they don't publish original research.
If you have answered "yes" to these five questions you have probably located a scientific article.