Tutorials are for learning, and not so much for quick customizing for live use on your own site. As for the intended skill level of this tutorial:
http://www.phpwebcommerce.com/php-mysql-shopping-cart-tutorial.php wrote:
I have to assume that you already know about PHP and MySQL so i won't explain every code in detail.
If you want to learn about doing this sort of thing, by all means, continue.
On the other hand, if you're at the point where you're frustrated with "trying to get it to work" and you just want it ready for your site, I'd say it's time to hire a programmer to do it for you.