When a customer visits an e-commerce store, it is to search for or buy a product. Check-out does not happen once, it is in stages. From the point of finding a product to checking the description and details to adding them to the cart and finally paying for the items.
Check-out is the procedure a customer goes through to purchase an item from an e-commerce store. Check-out is more of a flow than a one-time act.
Example of a typical check-out process
Product search > product description and details > shopping cart > Shipping information > Billing and payment details > payment confirmation.