String txt = editText.getText().toString();
Intent intent = new Intent(LoginActivity.this, MainActivity.class);
intent.putExtra("login", txt);
startActivity(intent);

TextView txtEmail = (TextView) findViewById(R.id.tvEmail);
Bundle b = getIntent().getExtras();
if(b!=null){
    String email = b.getString("login");
    txtEmail.setText(email);
}