If you're asking what STFU means it is - Shut The F*** Up.
If you're asking why you need to do that, it's because you need to let your wife talk and get her thoughts and feelings out. You need to validate those to let her know that you're listening to her. Validating doesn't mean you agree with all she says, just that she has a right to feel the way she feels. Do not make the mistake of defending yourself either. Just listen.