Any Publons user can endorse a journal. A journal endorsement may indicate that the user has had a good experience either publishing in or reviewing for the journal, or simply that they believe they publish cogent, high-impact research.
Any number of journals are present on Publons with peer review practices ranging from the incredibly thorough to almost non-existent. In order to help users identify those journals with high quality publication and reviewing processes we ask the community to contribute endorsements to those journals they would recommend working with. You can read more about identifying predatory journals here.
When you find a journal you want to endorse, simply hit the "Endorse this Journal" button on the journal's detail page in order to add an endorsement:
You can view all the journals you've endorsed on the endorsements page of your private dashboard.