Create Shortcode in wordpress custom plugin

Sometimes, no matter how cool your theme or how incredible the visual editing plugin you are using is, there is a feature you want that they just don’t have. And the easiest way to add some really cool functionality into your site is with a shortcode.

custom_plugin.php

function shortcode_fun(){
   return 'this is custom shortcode';
}

add_shortcode('sc', 'shortcode_fun');

shortcode

[sc] // paste in any page
OR

<?php echo do_shortcode("[your_shortcode]"); ?>

function certificate_form_generate_fun(){

return 
'<form action="" method="post">
<input type="text" id="name" name="name">
<input type="text" id="email" name="email">
<button id="newsubmit" name="submit" type="submit">Save</button>
</form>';

}

add_shortcode('certificate_form', 'certificate_form_generate_fun');

function my_shortcode_fun($atts){
   $atts = array_change_key_case($atts, CASE_LOWER);
   // for manage case sensitive
   $atts = shortcode_atts(['msg' => 'include("abc.php")'], $atts); 
   // return a value should be equal to $atts
   
   return "Hi this is my shortcode ".$atts['msg'];
}

add_shortcode('my_shortcode', 'my_shortcode_fun');

[my_shortcode msg="hi pankaj"]
// Hi this is my shortcode hi pankaj

[my_shortcode] 
// Hi this is my shortcode hello pankaj

[my_shortcode MsG="check case"]
// Hi this is my shortcode check case (its working)