//Getting instance FirebaseFirestore db = FirebaseFirestore.getInstance(); //Creating and initializing User object User user = new User("user1234","waqas","younis","first","january","1990"); //Getting Reference to "users" collection CollectionReference collectionReference = db.collection("users"); //Getting reference to "new doc" document DocumentReference documentReference = collectionReference.document("new doc"); //Writing data documentReference.set(user);