If a journal is peer-reviewed (often referred as refereed) then it has a process for experts in the field of the journal to evaluate/review the articles proposed to the journal before they are published.
If you found the journal in the library database Scopus, then the journal is peer-reviewed as everything in Scopus is peer-reviewed. If another source then you will want to check the journal's website. Often the journal will have information on the peer-review process, if there is one, under the About section of the journal.