plugin.js

(function($){
  $.fn.testPlugin = function(options){
    var opts = $.extend({}, $.fn.testPlugin.defaults, options);
    
    var insideFunction = function(){
      alert('hi!')
    }
    $fn.testPlugin.callInsideFunction = insideFunction
    
    return this.each(function(){
      
    })
  }
  
  $.fn.testPlugin.defaults = {
    
  }
})(jQuery);

// later...

$.fn.testPlugin.callInsideFunction()