Execute Script When Anchor Tag is Clicked?

[Glese]

How can I achieve the following scenario with an anchor tag?

 

if(isset($_POST['submit'])) {
     // execute script
}

 

I do need it for a label system to sort content with labels.

[trq]

<a href="?foo">click foo</a>
<?php
if (isset($_GET['foo'])) {
  echo "Do something foo";
}