Do I need a card to start the trial?

No card goes into nouz. You install nouz from the Shopify App Store and choose a plan on Shopify's own plan page. Its charge goes on the Shopify bill you already pay. The 14-day free trial starts when you approve the plan. Nothing is charged until the trial ends.

If you change your mind, cancel during the trial and you pay nothing. Use Cancel plan in nouz, under Settings and then Billing. You can also uninstall nouz from your Shopify admin before the trial ends. Uninstalling also disconnects your store, and its synced orders are deleted 48 hours later.

A few stores signed up on nouz.co before nouz was in the App Store. They entered a card with Stripe, a payment company, when they signed up. They keep paying that way, and they manage it under Settings, Billing.