If by "what's required from an open source license" you mean "what are the requirements from a license so it can be considered an open source license", the OSI website provides a definition of open source. By definition, a license that isn't listed as approves by OSI is not an open source license (although that doesn't mean such licenses can't be used, or don't have other merits, of course!).
If by "what's required from an open source license" you mean "what is required from me in order to use license XYZ", I think you meant https://choosealicense.com/. Several other sites, most notably, GitHub (when you click through a project's license), also take their definitions from there.