jQuerty functions.js what is this for ?

jQuerty functions.js what is this for ?

Hi, here is the code I have in that file. I started reading the tutorial just in the beginning and there was explaining where I need to write my functions after the ready event. Ok but with with HTML5 Reset I have this index.html page setup with jQuery:
 
  1. <script src="http://ajax.googleapis.com/ajax/libs/jquery/1.5.1/jquery.min.js"></script>
     <script>!window.jQuery && document.write(unescape(''))</script>
     <script src="js/functions.js"></script>

And I was wondering why do I have this functions.js file. Looks like it's some kind of a start up file in which I should start writing my jQuery code and one of the comments suggest that is the same as the ready event. But I don't get any of this. Why do I need a namespace. I see it declared but not used. The next line starts with (function($) { ... really ? with "(" ? I am kinda new to javascript, did a lot of flash, but I really don't get this.
Could someone explain me what are these lines below for please? And maybe any guide where can I look up this syntax so I begin to understand what is going on... Thanks a lot in advance !!! :)
  1. /* Declare a namespace for the site */
    var Site = window.Site || {};
  2. /* Create a closure to maintain scope of the '$'
       and remain compatible with other frameworks.  */
    (function($) {
     
     //same as $(document).ready();
     $(function() {
      
      






  3.  });

  4.  $(window).bind("load", function() {
      
      
     
     });
     
    })(jQuery);