class My_Widget extends WP_Widget {
    function My_Widget() {
    //Constructor
    }
    function widget($args, $instance) {
    // prints the widget
    }
    function update($new_instance, $old_instance) {
    //save the widget
    }
    function form($instance) {
    //widgetform in backend
    }
    }
    register_widget('My_Widget');

Wordpress Widget Structure

wordpress

PHP