TextToSpeech convert your text into voice. Android provide TextToSpeech class, here we need to instantiate an object of this class and also specify the InitListener. Below code will describe you how to create Text to speech app.

public class MainActivity extends Activity implements
        TextToSpeech.OnInitListener {

    private TextToSpeech tts;
    private Button btn;
    private EditText txt;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        tts = new TextToSpeech(this, this);

        btn = (Button) findViewById(R.id.button1);

        txt = (EditText) findViewById(R.id.editText1);
        btn.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View arg0) {
                speak();
            }

        });
    }

    @Override
    public void onDestroy() {
        if (tts != null) {
            tts.stop();
            tts.shutdown();
        }
        super.onDestroy();
    }

    @Override
    public void onInit(int status) {
        if (status == TextToSpeech.SUCCESS) {
            int result = tts.setLanguage(Locale.US);
            if (result == TextToSpeech.LANG_MISSING_DATA
                    || result == TextToSpeech.LANG_NOT_SUPPORTED) {
                Log.e("TTS", "This Language is not supported");
            } else {
                btn.setEnabled(true);
                speak();
            }

        } else {
            Log.e("TTS", "Initilization Failed!");
        }

    }

    private void speak() {
        String text = txt.getText().toString();
        tts.speak(text, TextToSpeech.QUEUE_FLUSH, null);
    }

}