How many products are you planning on selling? Are they unique or standardized? (e.g. art & crafts or board games)
For a high number of standardized products, I would recommend OpenCart ( http://OpenCart.com ), which is a simple free and open source eccomerce solution. It's really great, however, it is complex. But, if you're planning to make a big business out of it, in my experience it's the best way to go.
If you are selling a few or unique products and want a lighter weight solution you could use WordPress with plugins if you don't want to get in really deep to the complexities of OpenCart.
If you do use WordPress use this plugin: http://www.tipsandtricks-hq.com/wordpress-simple-paypal-shopping-cart-plugin-768 or any of these for a little bit more complex thing: http://sixrevisions.com/wordpress/top-5-excellent-e-commerce-plugins-for-wordpress/
With either method you will need hosting, a domain, and a theme which is explained by http://ThisIsHowYouMakeAWebsite.com
You can find additional themes on the OpenCart website of you choose to go with that: http://www.opencart.com/index.php?route=extension/extension&path=1
Once you get those you will also need to make the decision about payment gateways [ http://en.wikipedia.org/wiki/Payment_gateway ]. Will you use one or just PayPal Basic/Google Checkout? If so who? OpenCart and the WordPress plugins support a number. If you do decide to use a gateway you will also need a dedicated IP & Secure Certificate which are available thorough the host recommended by http://ThisIsHowYouMakeAWebsite.com