How to return to MainActivity

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_contact_form);

    ((Button) findViewById(R.id.btnOK)).setOnClickListener(new View.OnClickListener() {
        public void onClick(View v) {
            sendEmail();
        }
    });
}


private int Send_Email_Request = 1;

private void sendEmail() {
    String to = ((EditText) findViewById(R.id.txtTo)).getText().toString();
    String number = ((EditText) findViewById(R.id.phoneNumber)).getText().toString();
    String mess = ((EditText) findViewById(R.id.txtMessage)).getText().toString();
    Intent mail = new Intent(Intent.ACTION_SEND);
    mail.putExtra(Intent.EXTRA_EMAIL, new String[]{to});
    mail.putExtra(Intent.EXTRA_SUBJECT, number);
    mail.putExtra(Intent.EXTRA_TEXT, mess);
    mail.setType("message/rfc822");
    startActivityForResult(mail, Send_Email_Request);
}