Button that calls another screen and another button on the new screen that returns to the old screen

  

Screen 1

final Button myButton = (Button) findViewById(R.id.myButton);
myButton.setOnClickListener(View.OnClickListener {
    @Override
    public void onClick(View v) {
        Intent i = new Intent(this@Tela1, Tela2.class);
        startActivity(i);
    }
});

  

Screen 2

You can use any button or even set a navigation button on your Toolbar .

 <android.support.v7.widget.Toolbar
            android:id="@+id/toolbar"
            android:layout_width="match_parent"
            android:layout_height="?attr/actionBarSize"
            android:background="#fff"
            app:navigationIcon="@drawable/ic_back" /> <!-- este é o icone de navegação -->

And in the Screen 2 class:

final Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);

toolbar.setNavigationOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View v) {
        finish();
    }
});

You can also use any button that will have the same result. What happens above is that you start a new Activity , but the previous one remains in Stack , that is, it has not been finalized, only paused. Then, giving finish , it reopens because it has remained in the queue for activities .

Feel free to ask new questions in the comment for this answer, should you have any questions.