The app was scheduled for a launch on the 21st of July, but it seems that someone might have pulled the trigger a bit earlier than expected because the app is now available for download for both iOS and Android devices. That being said, it seems that there’s not much that one can do with the app at the moment since Splatoon 2 is the only game that will fully support it at the moment.
We expect that other games will be supported in the future, but for now if you don’t own Splatoon 2 then we guess you won’t really be using the app all that much yet. Do take note that according to Polygon, it seems that Nintendo is working on stabilizing the app’s servers which means that you might experience some connectivity issues for now, but presumably it will stabilize eventually.
Once it does, users will be able to log into the app with their Nintendo Account that is associated with their Switch console. If you haven’t linked your Account with your Switch console, then perhaps now is a good time to do so.