There are several good sites explaining the characteriztics of a scientific article:
Are you wondering if an article or book has been peer-reviewed? For both document types, you can use the register of scientific journals and publishers to check. Search by journal title or publisher name, e.g. Gyldendal Akademisk and check if it's on level 1 or 2:
All publications from journals and publishers on level 1 and 2 are peer-reviewed.
If you cannot find the journal title or publisher's name in the register, you can often find information about peer review on the journal's or publisher's website.