Everything you'll see and find on this portal is published under a CC-BY licence: "Creative Commons", Open Access, of the type "BY".
CC-BY is the standard "Creative Commons" licence, and imposes just one condition: "Attribution". This is explained in their informative flyer as follows:
Attribution: All CC licenses require that others who use your work in any way must give you credit the way you request, but not in a way that suggests you endorse them or their use. If they want to use your work without giving you credit or for endorsement purposes, they must get your permission first.
Concretely, this means for material to be found on the portal:
If the page in question is attributed to an author and features a publication date, "Philosophie.ch", the author and the date must be mentioned if the material is used. Additionally, a clickable link to the publication of the portal should be included.
If the page has a DOI, then the DOI replaces the link, and should be mentioned as well.
In this way, your work is protected from plagiarism: you can credibly and verifiably claim to be its author, and you retain the right to reuse it in any way you want, republish it, sell it, repackage it, offer it to someone else - it's yours.
More information available here.