make custom queries using sequelizejs

I am using sequelizejs orm in my nodejs app. And I dont have its documentation mentioning how to make custom sql queries. I found an example by googling but couldnt understand its syntax. and what the role of this callee function.

  var callee = {
                    build: function(result, config) {
                        console.log("callee", result);
                    }
                };
                sequelize.query("SELECT * from Users", callee).on("success", function(){
                    console.log("success");

                });