i think You want to use the DateTimePicker control in your Windows Forms program.
dateTimePicker1_ValueChanged. This event handler is very useful on the DateTimePicker. Whenever the user changes the DateTime, this event handler is executed.
try this way :
private void dateTimePicker1_ValueChanged(object sender, EventArgs e)
{
DateTime result = dateTimePicker1.Value;
TExtbox1.Text= = result.ToString();
}