Same way you would with the Button events.
In your UserControl, it would look something like this:
public event DateRangeEventHandler DateChanged {
add { monthCalendar1.DateChanged += value; }
remove { monthCalendar1.DateChanged -= value; }
}
Then in your form, like all controls with events:
userControl11.DateChanged += userControl11_DateChanged;
void userControl11_DateChanged(object sender, DateRangeEventArgs e) {
// do something...
}