USCIS will update your case if to let you know that you case has been sent to NVC for further process (they dont always do that). Or will you receive an email from NVC that they have your case and CASE ID and Invoice ID assigned. When you are able to log in you have to pay first, only then when payment processed you can start your applications otherwise you cannot do anything. When making payments just know that you can only pay one at a time.