public partial class MainWindow : Window, INotifyPropertyChanged
    {
        private string toTextBox;
        public string ToTextBox
        {
            get { return toTextBox; }
            set { toTextBox = value; this.OnPropertyChanged("ToTextBox"); }
        }

        private ObservableCollection<People> peoples;
        public ObservableCollection<People> Peoples
        {
            get { return peoples; }
            set { peoples = value; this.OnPropertyChanged("Peoples"); }
        }

        public event PropertyChangedEventHandler PropertyChanged;

        protected virtual void OnPropertyChanged(string name)
        {
            var eve = this.PropertyChanged;
            if (eve != null)
                eve(this, new PropertyChangedEventArgs(name));
        }

        public MainWindow()
        {
            InitializeComponent();
            this.ToTextBox = "Тектс в тексбоксе";
            this.Peoples = new ObservableCollection<People>() { new People() { FIO = "Ivanov Ivan Ivanch" }, 
                                                                new People() { FIO = "Ivanov2 Ivan2 Ivanch2" }};
        }

    }

    public class People
    {
        public string FIO { get; set; }
    }

 <Grid>
        <StackPanel>
            <TextBlock Width="100" Height="30" Text="{Binding Path=ToTextBox, ElementName=__Main}" ></TextBlock>
            <ListBox Width="200" DisplayMemberPath="FIO"  Height="200" ItemsSource="{Binding Path=Peoples, ElementName=__Main}"></ListBox>
        </StackPanel>
    </Grid>