Another question from the same class. Woo Commerce is an e-commerce toolkit that you can use to add a storefront to a WordPress-based website. Click here to watch the introductory video. It looks pretty cool.
However, if you have uncommon needs, like the ability to sell and ship to addresses outside the U.S., check carefully that Woo Commerce can support them. You can waste a lot of time and some money getting set up, and then discover the cart doesn’t work for your customers (which one of our clients discovered after installing a well-reviewed cart).