When we think of "finding an article" we often think of newspapers or magazines. But there are several kinds of articles your assignments might require:
News - From newspapers reporting daily events (New York Times)
Magazine - Often called "popular" articles, these are general or for a specific interest (Time, Discover)
Trade - By and for specific industries (Advertising Age)
Scholarly - Reporting research, written by and for scholars and researchers (American Journal of Psychology)
See the chart below for more information on how to tell if an article is scholarly or popular.