If you want, for example, to show in a text box loop iterations in a real time, then you have to use something like:
Dispatcher.CurrentDispatcher.Invoke(DispatcherPriority.Background, new Action(
() =>
{
DisplayCount = i.ToString();
OnPropertyChanged(() => this.DisplayCount);
System.Threading.Thread.Sleep(10);
}));
Where DiplayCount is property to which TextBox is binded. Here I explained how to use INotifyPropertyChanged, and from here you can download example.