Peer reviewed journal articles undergo independent review by one or more experts in the field before publication. These "referees" look for valid research methodology and accurate data, but do not necessarily support the conclusions of the author(s).
Published peer-reviewed articles have been vetted for quality and importance so they should be reliable sources to use in your own research and writing.
Be aware that only the scholarly content in these journals is peer-reviewed - news items and opinion pieces might also be included in the journal, but not reviewed.