output html on post or page from custom plugin [closed]

To create shortcode write code in the your theme file functions.php

 function my_shortcode_fun() {
        $output = $class="";
        ob_start(); 
            enter code here....
        $output = ob_get_contents();
        ob_end_clean();
        return $output;
    }
    add_shortcode('my-shortcode', 'my_shortcode_fun');