You can authenticate your users in your app with firebase. This example will helps you to make signup and login forms. hen users information can easily send to firebase. I explained everything on my blog. If you want to learn how it make step by step you can visit my blog.
Medium Blog: https://medium.com/@erguloguz/react-native-firebase-email-authentication-1a2f1d2c5fc1
LinkedIn: https://www.linkedin.com/in/oguzergul