Ecommerce stores should enable ecommerce tracking in analytics. This allows you to relate your analytics figures to your sales figures, and gives some different but complimentary reports not available in the Zeald ecommerce reports.
for enabling ecommerce tracking
Please note, the Zeald software will automatically add the code required to the receipt page that the google docs refer to, adding the details of the items purchased, prices etc. You don't need to perform any of the steps google recomends about adding code to your site (eg adding calls to _addTrans()) - this is done for you already by the system.
One circumstance where this might not work is if you have a customised ecommerce system that doesn't make use of standard Zeald Ecommerce system, eg customisations that completely change the order experience, or ones that modify the receipt page. These would need to be specifically built to support the ecommerce tracking.
If in doubt, or if there's any problems with ecommerce tracking, check with Zeald support.