To add a redirect with php is very simple.

Open your text editor, i recommend notepad ++ Which is free.

copy and paste this code into the blank file

<?php
header( 'Location: http://www.YOURSITE.com' ) ;
?>

Change the YOURSITE to the location you want to redirect to, save this as index.php and upload, job done :-)

Reasons why you may want to use this, your site is in the catalog folder and you have nothing in your root, so when you call www.yourstore.com you get a blank page set the redirect to www.yoursite.com/catalog and it will redirect to the catalog folder.

Please note this must be a temporary thing or your SEO ranking will suffer!