How to put a subtitle under the application name in the bar menu

For this you must register a listener for when the ViewPager item changes you capture the event and do something related.

This can be done like this:

ViewPager galeria = (ViewPager) findViewById(R.id.galeria);
galeria.setOnPageChangeListener(new ViewPager.OnPageChangeListener() {
    @Override
    public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
    }

    @Override
    public void onPageSelected(int position) {
        getActionBar().setTitle("Posição "+position);
        getActionBar().setSubtitle("Posição "+position);

        // Para biblioteca de compatibilidade
        //getSupportActionBar().setTitle("Posição "+position);
        //getSupportActionBar().setSubtitle("Posição "+position);
    }

    @Override
    public void onPageScrollStateChanged(int state) {
    }
});

To change according to the adapter item you can also create a method that searches for it by passing the received position in onPageSelected() and then change its title and subtitle immediately.

In your Activity , use the code below to set the title and subtitle if you are using ActionBar :

getActionBar.setTitle("Título");
getActionBar.setSubtitle("Subtítulo");

Or getSupportActionBar if you are using the compatibility library.