A periodical can be a newspaper, magazine or scholarly journal. The type of information you need determines which types of periodicals you should use. Newspapers and magazines are good for finding current event information.
Scholarly journals contain in-depth information on a subject, including reports of research.
Articles found in scholarly journals are reviewed by other professionals in the same field as the author before they are published. Journal articles are usually focussed on a very specific topic and contain useful bibliographies of other sources dealing with the same topic. To obtain periodical information, the library subscribes to many databases, both general and subject specific.