How to navigate from one screen to another screen

OnClickListener onClickListener = new OnClickListener() {
    @Override
    public void onClick(View v) {
        startActivity(new Intent(action));
    }
};

Button button = (Button) findViewById(id);
button.setOnClickListener(onClickListener);

Button x.setOnClickListener(new View.OnClickListener() {
    public void onClick(View v) 
    {
        Intent i = new Intent(y.this, Activity.class);
        startActivity(i);                   
    }
});

Here we've defined a listener for Button x. The OS will call this method and start the Activity referenced in Intent i.

Here's the official tutorial example: http://developer.android.com/guide/tutorials/notepad/notepad-ex2.html

The most trivial case (called from activity):

startActivity(new Intent(this, ActivityToLaunch.class));

More details here: http://developer.android.com/guide/topics/fundamentals.html