Scholarly articles accepted for publication in a "peer reviewed" journal have been analyzed by experts with deep knowledge of the subject. These "peers" will have reviewed the paper, including its assumptions, research question, literature review, methodology and results, and have assessed the findings to determine the originality and soundness of the research presented for publication. Once the peer review process is complete, the article can be accepted it for publication as is, be revised before publication, or be rejected altogether. Think of peer review as a quality control process.
Check if Journal Follows the Peer Review Process
Ulrichsweb will tell you if a journal follows the peer review process or not.
If you are not sure how to use Ulrichsweb, see this Ulrichsweb Instructions PDF.