Evaluating sources is an ongoing part of the research process. Continual evaluation of sources will allow you to produce a better project. Part of the evaluation process involves identifying the various types of articles such as popular/general interest, trade/professional and scholarly.
Scholarly articles are usually written by specialists in their fields, and they have descriptions of methods of research and extensive bibliographies or lists of references at the end of the articles. These articles have been reviewed by the authors' peers in the field to make sure the research was conducted in a scholarly manner.
Trade publications usually provide short articles written for people interested in a specific industry. They often have the latest news and trends and sometimes job advertisements.
(More in the Library Research Tutorial)