Scholarly articles are written by experts in the field and, additionally, peer reviewed by a panel experts in the field. They tend to include a lot of research and data, and the information in the article is backed up by a list of references.
Example of a Journal with Scholarly Articles
Popular articles are often written by journalists for a general audience and are not reviewed by experts in the field. Popular articles rarely include references.
Example of a Magazine with Popular Articles
For more detailed information on what a scholarly article looks like, see the excellent tutorial Anatomy of a Scholarly Article.