I need to add the code shown here:
To my WooCommerce "Thank You" page, that customers get sent to, after a successful sale.
Not entirely sure how to add the code, since Wordpress doesn't really like adding code on pages.
Woocommerce allows you to override the default templates by creating a copy inside your theme folder. Once you create the copy you can insert a function to add the appropriate code to the page.
So create a folder called 'woocommerce' inside your theme
Inside that folder create another folder called 'checkout'
Copy the file thankyou.php file from /wp-content/plugins/woocommerce/templates/checkout/ folder to your new 'checkout' folder in your theme
Once you do that you can add your code to the new thankyou.php file. This is what it could look like if you want to just insert it with the page content: http://pastie.org/8137912
Although, many themes have an extra hook for right before the closing </body> tag, which is the ideal place to put the code. If yours does you can insert your code with a function on the template.