Alexa adds a selection for that item to your cart. Follow the prompts to place your order. Some items, require completion using the Amazon app or on the Amazon website. Or, say, “Checkout my cart,” and follow the prompts to check out your order. If you no longer want the order, say “Cancel my order.”
https://www.amazon.com/gp/help/customer/display.html?nodeId=GFEBUXE7DH7G9EQ4