Making functions in JQuery

Making functions in JQuery

I feel like using too much classic javascript, and really like to encapsulate my functionality in JQuery.

For example I have the following JS function:

        function DoStuff(param) {
           // Do stuff with param
            return foo;
        }

from a JQuery button click I do like this.
 $("#btnMyButton").click(function () {
             //Do stuff
             DoStuff(myParam);
           
              // Do some other stuff               

            });

What is the best way to define a JQuery function and call it?
I found this notation:
(function( $ ){ $.fn.myfunction= function() { alert('hello world'); }; })( jQuery );

and then the example says to call it like:


$('#my_div').myfunction();

But how can I call my DoStuff function without having a div or anything else. 
I just want to call it like this: 



$.DoStuff