A successful checkout fires the store's "order_create" marketing automation trigger (e.g. Klaviyo), which typically drives the customer confirmation email/receipt — the exact wording and any SMS are controlled by the store's own marketing templates, not a fixed system email. You're also redirected straight to your order's detail page (/checkouts/{id}), which shows a "thank you" state. (Separately, the store's staff get their own internal new-order notification — that's not something you as the customer receive.)