Need assistance to understand a piece of code
<p>I'm having difficulties to understand the code below taken from this page <a href="http://trevordavis.net/play/jquery-one-page-nav/" rel="nofollow">http://trevordavis.net/play/jquery-one-page-nav/</a> (tutorial for one page websites). Especially the .do and the Lorem ispum text in the middle of the code and also the reference to section-4. Could you shade some light on that? Many thanks</p>

<pre><code>&lt;script src="jquery.js"&gt;&lt;/script&gt;
&lt;script src="jquery.scrollTo.js"&gt;&lt;/script&gt;
&lt;script src="jquery.nav.min.js"&gt;&lt;/script&gt;
&lt;script&gt;
$(document).ready(function() {
  $('#nav').onePageNav();

  $('.do').click(function(e) {
    $('#section-4').append('&lt;p&gt;Lorem ipsum dolor...&lt;/p&gt;');
    e.preventDefault();
  });

});
&lt;/script&gt;
</code></pre>
