Every database approaches this issue differently if they have peer reviewed content in it. Here are some strategies to focus in on the peer reviewed content in a database. (Note: it's a good idea in general to verify that an article you find is peer reviewed even if you use these, as a double check).
These are the 2 main ways that databases allow you to limit to peer reviewed materials. If you don't see something like that, it's possible that it's not an option in the database you're using, or the content in that database is either all peer reviewed or none of it is peer reviewed.
Sometimes you either have to use a database where they don't have an option, the existing option is ambiguous. So what do you do in that case?
It requires a little investigation, but there are ways that you can find out if an article is Peer Reviewed