Beginner question. what does this createhostbuilder do?

 public static IHostBuilder CreateHostBuilder(string[] args) =>
            Host.CreateDefaultBuilder(args)
                .ConfigureAppConfiguration((hostingContext, config) =>
                {
                    config.AddKeyPerFile(directoryPath: Path.Combine(Directory.GetCurrentDirectory(), "secrets"), optional: true);
                    config.AddKeyPerFile(directoryPath: Path.Combine(Directory.GetCurrentDirectory(), "platform-secrets"), optional: true);
                })
                .ConfigureWebHostDefaults(webBuilder =>
                {
                    webBuilder.UseStartup<Startup>();
                });
    }