how to create wordpress shortcodes

1function create_shortcode(){
2    return "<h2>Hello world !</h2>";
3}
4add_shortcode('my_shortcode', 'create_shortcode');
5// Use [my_shortcode]

1// function that runs when shortcode is called
2function wpb_demo_shortcode() { 
3 
4// Things that you want to do. 
5$message = 'Hello world!'; 
6 
7// Output needs to be return
8return $message;
9} 
10// register shortcode
11add_shortcode('greeting', 'wpb_demo_shortcode'); 

1function wp_demo_shortcode() { 
2
3//Turn on output buffering
4ob_start();
5$code = 'Hello World';
6ob_get_clean();
7
8 // Output needs to be return
9return $code;
10} 
11
12// register shortcode
13add_shortcode('helloworld', 'wp_demo_shortcode'); 

1// function that runs when shortcode is called
2function wpb_demo_shortcode() { 
3 
4// Things that you want to do. 
5$message = 'Hello world!'; 
6 
7// Output needs to be return
8return $message;
9} 
10// register shortcode
11add_shortcode('greeting', 'wpb_demo_shortcode'); 
12