Remove text after clicking in the textbox

Question

When you activate an application, a textbox with text \"hello\" will appear.

My question is:
When you click on the textbox in order to make input data, I want to rem

Answer 1

I want to update Donut's answer.(applicable for windows 8)

Code behind code be

public void TextBox_GotFocus(object sender, RoutedEventArgs e)
{

   TextBox tb = (TextBox)sender;

   if(tb.Text != "SOME DEFAULT TEXT")
   {

     String persentContentWithDefaultString = t.Text as string;
     tb.Text = persentContentWithDefaultString[0].ToString();
     // set cursor position 
      tb.Select(1, 0);         

      tb.GotFocus -= TextBox_GotFocus;
 }
}

Actully in my page , there were two textbox and one button. [Username,pass,and click button]. By default , focus goes to my first textbox and User was not able to see the default text.