In order to checkout, click the cart icon on the upper right of your screen if not already in the checkout process. When you click "Check Out", this is the screen you see. It shows you everything that you have in your cart and the quantities. You can choose to add quantities and update your cart, Remove Items from your cart, continue shopping or continue checkout from here.

https://www.northernfactory.com/UserFiles/Images/Category/Website%20Design/Navigation/CheckoutX.png