What is the difference between a popular source such as a magazine and a peer reviewed source / journal?
Magazines are written for the general public. They often have a lot of advertisements in them.
Journals, on the other hand, are targeted to students or professionals working in a particular field. The usually have very few ads in them. The articles usually include bibliographies at at the end and the author's or authors' credentials (where they went to college and where they work) are given.
Sometimes a publication is peer-reviewed which means that all of the articles have been read and approved for publication by experts in the field.
Peer reviewed materials are excellent sources of information for scholarly papers!
Peer reviewed = Articles read & approved for publication by experts in the field
Experts = People with advanced degrees in the subject or who have worked in the field for many years