CORS is a browser safety rule that lets a website say which other websites may request information from it. It is like a front desk checking whether a visitor is allowed to receive a particular file.
If a page tries to read data from another address, the browser checks whether that site's response allows it. This can prevent an unrelated website from quietly reading certain information.
CORS is mainly a rule for website developers and servers to configure. It is not a general login system, and changing settings in a visitor's browser is usually not the right fix.