What exactly do you mean that it shows an iPod menu? That would sound like you are not connected to CarPlay, but to the media section of the vehicle's sound system. Have you asked your Nissan dealer about this? Understand that CarPlay is a system, and that Apple provides the connection, but the vehicle dealers determine the way their vehicles react to the system and display information.
Do you have more than one USB connector for the vehicle? Is it possible that you are not plugged into the one for CarPlay, but for other media? Can you check your Owner's Manual, or again, check back with the dealer. They should be able to walk you through using all of their vehicle features.