One of the most common questions we get from Joomla learners is ... How do I set up a shopping cart with Joomla?
For several years the only option was Virtuemart. However, Virtuemart is a very large and complex product that it simply overkill for many sites.
Fortunately, some simpler and easier shopping carts have recently been released and perhaps the best of the bunch is RokQuickCart from Rockettheme.com.
It does have basic tax and shipping options, plus support for either PayPal or Google Checkout. It doesn't have the ability to put products into categories or have custom fields for products (except color and size). Really it's ideal for a website selling up to 20 or 30 products.