Saving login and password in the application (Android Studio)?

Question

Java

How to save the login and password of the user who entered his data when logging in, for example, to his page? I just know that SharedPreference should be used here, but I don't know how to insert it into my code correctly.
here is the code:

@Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_password_em);
        
        mAuth = FirebaseAuth.getInstance();

        ETemail = (EditText) findViewById(R.id.et_email);
        ETpassword = (EditText) findViewById(R.id.et_password);

        findViewById(R.id.btn_sign_in).setOnClickListener(this);
        findViewById(R.id.btn_registration).setOnClickListener(this);

    }

    @Override
    public void onClick(View view) {

        if(view.getId() == R.id.btn_sign_in)
        {
            signin(ETemail.getText().toString(),ETpassword.getText().toString());
        }else if(view.getId() == R.id.btn_registration)
        {
            registration(ETemail.getText().toString(),ETpassword.getText().toString());
        }
    }
    public void signin(String email, String password) {
        mAuth.signInWithEmailAndPassword(email, password).addOnCompleteListener(this, new OnCompleteListener<AuthResult>() {
            @Override
            public void onComplete(@NonNull Task<AuthResult> task) {
                if (task.isSuccessful()) {
                    Toast.makeText(PasswordEM.this, "Авторизация прошла успешно", Toast.LENGTH_SHORT).show();
                    Intent intent = new Intent(PasswordEM.this,ListTasks.class);
                    startActivity(intent);

                } else
                    Toast.makeText(PasswordEM.this, "Авторизация провалена", Toast.LENGTH_SHORT).show();
            }
        });
     }
    public void registration(String email,String password){
        mAuth.createUserWithEmailAndPassword(email,password).addOnCompleteListener(this, new OnCompleteListener<AuthResult>() {
            @Override
            public void onComplete(@NonNull Task<AuthResult> task) {
                if (task.isSuccessful())
                {
                    Toast.makeText(PasswordEM.this, "Регистрация прошла успешно", Toast.LENGTH_SHORT).show();
                }
                else
                    Toast.makeText(PasswordEM.this, "Регистрация провалена", Toast.LENGTH_SHORT).show();
            }
        });
    }
}

Answer 1

You must not store your username and password.