I have a react-native social media app. It lets user sign up and create password. It stores the user authenticated email in firebase database.
My question is, how can I make user verify if the are not using someone else's email.
i don't know if you are using Cloud Firestore ou Realtime Database but you can set rules for this checking email before write into db see more info here
see also firebase auth
You'll want to send a verification email to the user, and then check the emailVerified property in their user profile.
To send the email from the JavaScript SDK, see Send a user a verification emailSend a user a verification email in the documentation. If you're using react-native-firebase, the method can be found here.