how to start jquery function code example

Example 1: jquery document ready

The .ready() method is typically used with an anonymous function:
$( document ).ready(function() {
  // Handler for .ready() called.
});

Which is equivalent to the recommended way of calling:
$(function() {
  // Handler for .ready() called.
});

Example 2: how to create jquery function

(function( $ ){
   $.fn.myfunction = function() {
      alert('hello world');
      return this;
   }; 
})( jQuery );

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