How to stop record from submit in user event before submit? And also how to show popup message in user event before submit? Any idea??

You cannot show a popup in before submit, you could in a client script in onSave but that would only run in edit/create not view. You could also return false to prevent saving. To prevent saving in before submit you would need to throw an uncaught error. It's ugly but works. You could potentially on Create intercept the save, re-direct to the record, which would avoid changes being saved and in beforeLoad display a banner type message.