How to use explode and implode function

//explode function 

<?php
$string="WWW rootitech com";
$explode=explode(" ",$string);
$mini=2-2;
echo $explode[$mini];
 ?>

//explode and implode function

<?php
$string="www.rootitech.com";
$explode=explode(".",$string);
$implode=implode($explode,"@");
echo $implode;*/
?>