Check out this video to see how easy it is to start selling from free WordPress blogs at www.wordpress.com with Santu.
You can find the buttons added to the blog in this video at http://santulinks.wordpress.com/easy-selling-on-wordpress-com/
If you want to see how far you can take WordPress blogs with Santu, check out http://santu.com/total-design-freedom-with-sell-anywhere-links/ - although that goes beyond what you can do on a free WordPress blog.
Of course you can use the same sell anywhere buttons to sell your products via FaceBook, websites, Pinterest and more.
If you use a WordPress Blog to sell your products, you can also make the Continue Shopping button go back to your WordPress Blog instead of to your free Santu store. Yuo can adhust this here: http://app.santu.com/buynow/store/miscellaneous.