Sources available to you as you conduct research will vary quite a bit in purpose, audience, and reliability. One important distinguishing characteristic is whether a periodical is considered popular or scholarly (also called academic). You will need to learn how to tell them apart, as well as determine which type is more appropriate for your information needs.
All of us have seen these at one time or another. Think about the magazines you find in grocery, drug, and book stores. In popular magazines, you will generally find lots of advertisements and articles illustrated with several pictures. Popular magazines are written for the general public, usually for entertainment, general information, or keeping up with current events.
Popular magazines are normally written and edited by professional journalists. The authors who write the articles are usually not subject experts, but have hopefully done adequate and appropriate research in preparing for the article. The editor has final say on what gets printed in the magazine.
Academic/scholarly journals are written for students, faculty and professionals, and are usually considered to contain high quality articles. Research results are generally published in these periodicals. Limited advertising is geared toward the specific audience that would be reading the journal. Articles will only have pictures if they are important to the content, and not for decoration. Charts and graphs are common for presenting data.
Articles in academic/scholarly journals should be written by subject experts, as opposed to journalists that write for popular magazines. The editor who makes the final decision on what is published should also have expertise in the domain covered by the journal.
Peer-Reviewed Journals: Peer review adds an additional level of reliability. Not only are these articles written by subject experts, they are also reviewed by other subject experts for quality before being accepted for publication.
Trade Magazines are usually published by a professional organization for its members and others in the field.
Trade Magazines are generally written and edited by practitioners in a field.