While your first instinct should be to use scholarly sources in a college assignment, there are some contexts in which it is okay to use popular articles. If you are analyzing the different sides of an argument, it may be useful to reference different opinions that can be found in magazines or opinion pieces in a newspaper - but your main points should come from scholarly sources. Check out the article below from the Yale Poorvu Center for Teaching and Learning for more information on when it is useful to use different types of sources.
A popular magazine has articles written for the general public. They use easily-understood language and the articles tend to be short. Below are examples of popular magazines that you may be familiar with.
Check out "Structure of the Magazine" by Nikola Mileta for an in-depth description of the four elements a magazine: cover pages, the front, the feature well, and the back.
While popular magazines will follow their own publication's style guide and the "look" of the magazine, they typically contain the elements you see in the graphic below.
From Magazine Designing, 26 Mar. 2013.