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
Scientific articles are often difficult to read. Here's a great article on how to read and understand a scientific journal article:
How to Read and Understand a Scientific Journal Article by Jennifer Raff
Many articles are available for free: