What is the most efficient way to store user data for a mobile app? (Username, password, how much in game currency, total miles ran, scores for mini games, etc.)

I'm pretty beginner in the world of mobile app making – I'm using react native for the front end but I'm not sure what to use to store user data? I know SQL deals with tables and database storage but I saw someone mention MondoDB? Would anyone be able to point me to some good explanations or breakdowns?