Journals are collections of academic articles, mostly peer reviewed and therefore of good quality for academic research. Peer reviewed means that the articles have gone through a quality checking process by other researchers or academics before publication so you can be sure that the information is reliable. Articles are often the reported outcomes of research so tend to be on a discrete topic. They take much less time to publish than books although the peer review process can slow publication down.
Magazines and the professional press are mostly not peer reviewed and may not be the best source of information for you to use.
You can find journal articles in the articles tab on the library catalogue, the databases or even Google Scholar. The Library has very few printed journals, most are online.
You may find that your lecturer has provided links to key articles in the Reading Lists on your unit pages on SOL. But there is nothing to stop you researching more using the databases or articles tab - it could be the way to even better marks!
Once you have found an article make use of the work the author has put in - follow in their footsteps. Use the references he or she used in their research to generate further reading for you to follow up - but bear in mind they will be older than the original article.
Some databases will indicate where an article has been used in subsequent research - follow them up as well.
Google Scholar indicates where articles have been cited (used) by other researchers, allowing you to click and see these later works.