How to make firebase Realtime database writable according to authentic users

I am making an android app where anyone can read the data but only an authentic user (whom we added in Realtime database as ‘User’ with email id) can modify or add. I want that no one other than authentic user can write in his /her database. Others can only read.

Here is my database structure:-

Answer

Your rule might be

 {
  "rules": {
    "some_path": {
      "$uid": {
        // Allow only authenticated content owners access to their data
        ".read": "request.auth != null && request.auth.uid == $uid"
        ".write": "request.auth != null && request.auth.uid == $uid"
      }
    }
  }
}