First, you'll need to be able to identify a scholarly journal. Articles are written by scholars or experts in a field and they typically report on original research or experimentation. Articles are often long and start with an abstract and end with a list of cited sources. Peer-reviewed, or refereed articles, must be submitted to other experts in the field for review to ensure quality research.
Databases such as JSTOR and Science Direct contain scholarly journal articles. The EBSCOhost databases also have journal articles, but you must limit by source type to exclude magazine and newspaper article results. On your results list page, select the "peer reviewed" limiter under the search box. Make sure the article you choose isn't just a book review or news report from a journal - check the length and for the list of sources at the end.