Your instructor may require you to find "scholarly" sources. Scholarly and academic sources are articles/books that are written, researched and published differently than popular sources (news stories, commercial websites). Here are some features and attributes to look for to determine if it is a scholarly materials:

1. The article Includes a long list of references at the end 
2. The authors are experts in their field, their credentials such as their degree/certification that may be listed next to their names EXAMPLE: 'Michael Underhill, Ph.D.' 
3. The content will likely address a specific research question and report on their findings
4. The content of a scholarly article will be organized into sections e.g. "Introduction", "Abstract", "Research Methodology"
5. A scholarly article will be published in a "peer-reviewed" journal. Peer review is the process of evaluation from other experts in the same field as the authors