'Will' or 'Be going to'?

Will or Be going to! Do you know the difference? We use “be going to” to talk about future events that have been mentioned, decided, or planned before the moment of speaking. We use "will" to talk about future events decided at the moment of speaking (at the moment we make our decision). We use "be going to" to talk about an event based on evidence in the present (something we already see starting). We prefer “will” to make predictions or beliefs based on personal opinions.