Web of Science is an excellent tool for tracking down who has used a paper in their own research ("cited" or used as a reference.) Google Scholar has a similar "cited by" link that leads to a much wider (less selective) set of material. It is interesting to compare results.
Why cited articles are important: Psychological research is first presented by researchers in academic journals and books. (Sometimes, research with a general interest will get reported in magazines and newspapers and this can be a big help to understanding. See the tab Other Resource Types and Ideas.)
But most research grows out of the eye of public awareness. As research interest in a topic grows, there begins to be a group of scholars who begin to connect with each other in a pattern you can see. The pattern emerges in who they cite or refer to in their work.
This citation pattern is called an invisible college and if you am going to write about a topic, you should get some awareness of who these scholars and their works are. Some scholars rise to prominence and have research that most other scholars refer to as the most accepted research. These are the big names you should know.
So, look in two different directions-- at the older foundation works, the most accepted research, and the very new research to see who is being cited most now.
An article in a Peer Review journal (also called a "refereed journal" is one that has been looked at carefully before publication by experts in a scholarly field (the article author's "peers" in the profession) to determine if the article meets standards of research in a given field and allow it to be published. Peer reviewed or refereed is a mark of quality.
Articles that have been peer reviewed are claiming to be presenting original research, although it is no guarantee that the article is only presenting valid claims.
PsycINFO is a very large database with a mixture of sources. Google Scholar is even bigger. Although there is a filter for "Peer Reviewed" in PsycINFO, you might be better off starting your searches in databases that are limited almost entirely to peer reviewed journals. For example, the databases PsycARTICLES and Web of Science are good for this:
There are other things in peer reviewed journals that aren't considered research, such as editorials, letters to the editor, book reviews and announcements. These other things may turn up in a database even when you use a limit filter such as "Peer reviewed." If you have any doubt about something, ask your professor.
Publications that don't use peer review use the judgment of the editor to decide the quality of the article. These are usually only reporting on research done by researchers rather than the researcher presenting the research for the first time. Psychology Today and Scientific American Mind are examples of these kinds of publications.
Research databases index, describe, and add subject terms to articles-- all of which makes it easier to find relevant material. Look for Subject Terms or Descriptors in the database records, which you can click on or search for to narrow your search to articles primarily on your topic.
Search engines like Google Scholar don't have subject terms or descriptors added to records, but they do search full-text, so an unusual word might work to focus a search.