WordPress shortcodes are actually very easy to create. If you know how to write a basic PHP function, then you already know how to create a WordPress shortcode. For our first shortcode, let’s create the well-known “Hello, World” message.

1. Open the functions.php file in your theme. If it doesn’t exist, create one.
2. First, we have to create a function to return the “Hello World” string. Paste this in your functions.php file:
   function hello() {
return 'Hello, World!';
}
3. Now that we have a function, we have to turn it into a shortcode. Thanks to the add_shortcode() function, this is very easy to do. Paste this line after our hello() function, then save and close the functions.php file:
   add_shortcode('hw', 'hello');
4. Now that the shortcode is created, we can use it in posts and on pages. To use it, simply switch the editor to HTML mode and type the following:
   [hw]

That's all! Of course, this is a very basic shortcode, but it is a good example of how easy it is to create one.

Source: http://www.smashingmagazine.com/2009/02/02/mastering-wordpress-shortcodes/

Tags: WordPress Shortcodes