In certain databases, it's fairly easy to search for peer-reviewed articles. For ABI/Inform, make sure you've checked the box next to peer reviewed to search only for peer-reviewed articles (see below).
For Business Source Complete, the interface is a bit different but there's also a box to check for peer-reviewed articles (see below).
For Google Scholar and other databases that have no peer-reviewed box to check (make sure you have also clicked on "advanced search" as sometimes the box is hiding there), you'll have to do a bit more work. I'll use Google Scholar as an example, but you can do the same for any database.
You've searched in Google Scholar and you have a long list of results, you decide to use the last article. Underneath the title, you have the authors and the title of the journal, Gender and behaviour.
When you google the journal title, you will find the official website of the journal. To figure out if it's a peer-reviewed journal, you have to find the equivalent of "about us". In our example, it's "about this journal".
Then, you click on "Focus and Scope".
When you click on "Focus and Scope", you can see that it's a peer-reviewed journal. Be aware that most times, it will be written in the description of the journal.