It depend - if you want a whole shopping cart in your site, it does, but there are also a lot of option to get an online store without any technical knowledge.
If you are selling handmade items you can try set a shop on http://www.etsy.com, if you are setting something else, you can set an ebay store. Also, you can just make an HTML page in your site and add a paypal button for paying (check out http://www.paypal.com for more info about that).
The nicest ones I've seen that totally look like a part of your website are the yahoo store interface, they basically set it up for you, but it cost about 100$ a month.