How to save User Settings in WPF?

Look here

code:
   public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
            loadStuff();
        }

        public void loadStuff()
        {
            if (Properties.Settings.Default.ck1)
            {
                checkBox1.IsChecked = true;
            }
            else if (!Properties.Settings.Default.ck1)
            {
                checkBox1.IsChecked = false;
            }
           
        }    


        private void CheckBox_Checked(object sender, RoutedEventArgs e)
        {
            Properties.Settings.Default.ck1 = true;
            Properties.Settings.Default.Save();
        }

        private void CheckBox_Unchecked(object sender, RoutedEventArgs e)
        {
            Properties.Settings.Default.ck1 = false;
            Properties.Settings.Default.Save();
        }
    }