gistfile1.txt

       File aux = context.getFilesDir();

        String filename = "/myfile";
        String string = "Hello world!";
        FileOutputStream outputStream;

        try {
            File ins = new File(context.getFilesDir(), "INSTALLATION");

            FileOutputStream out = new FileOutputStream(ins);

            out.write(string.toString().getBytes());

            out.close();
        } catch (Exception e) {
            e.printStackTrace();
        }