So what goals are you going to track with Piwik? What do you want your website or business as a whole to do? Identifying your goals helps you define what success is in your business. In fact, the process of defining concrete goals may help you redefine or tweak what you thought were your business goals because it forces you to quantify those goals.
Piwik or any web analytics software cannot track anything that is not quantifiable. If you can't put a number on it, there is no way for a software to analyse it. Having happier customers next month sounds like a great goal in your mind, and may work as a mantra you repeat to yourself every morning, but to be a goal in Piwik, you need numbers. A customer's happiness factor cannot really be measured. But you can count how many orders are completed at your website, so finalized orders are a perfect goal. But this may not be your only goal. If you have a newsletter on your e-commerce site, another goal of yours could be newsletter signups...