(function($){...})(jQuery)

At the most basic level, something of the form (function(){...})() is a function literal that is executed immediately. What this means is that you have defined a function and you are calling it immediately.

This form is useful for information hiding and encapsulation since anything you define inside that function remains local to that function and inaccessible from the outside world (unless you specifically expose it - usually via a returned object literal).

A variation of this basic form is what you see in jQuery plugins (or in this module pattern in general). Since you are defining a function literal, it doesn't have access to anything from the outside world unless you explicitly pass in the information. Hence:

(function($) {
  ...
})(jQuery);

Which means you're passing in a reference to the actual jQuery object, but it's known as $ within the scope of the function literal.