Express middleware , could someone explain what every code line does?

** could someone explain what every code line does? **

 server.use(
        (req, res, next) => {
             res.header('Access-Control-Allow-Origin', 'http://localhost:3000');
             res.header('Access-Control-Allow-Credentials', 'true');
             res.header('Access-Control-Allow-Headers', 'Origin, X-Requested-With, Content-Type, Accept');
             res.header('Access-Control-Allow-Methods', 'GET, POST, OPTIONS, PUT, DELETE');
             next();
        }
    );