String papkablia = Environment.getExternalStorageDirectory() + "/W1/1.txt";
 FileOutputStream fos = new FileOutputStream(papkablia);
 String s = "аапопглрдшощжодшнгокнрло";
 fos.write(s.getBytes());
 fos.close();

<manifest ...>
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
...