To make an online purchase from Walmart.com, first create an account if you don't already have one by clicking "sign in" and "create an account" in the top right corner. Then use the search bar to find the product, add it to your cart, and at checkout enter your shipping address and payment information before confirming your order. Once purchased, the item will be delivered within the time frame selected, and customers can also leave a product review online after receiving their order.