Start by logging into your Google Checkout account (or opening an account if you don't have one).
The Product Block: This is a small, square product element. This is very suitable for creating a grid of products in conjunction with our 2-Column Element.
When you Publish your changes, the Add to Cart button should start working immediately.
What if you need to change your account Merchant ID used on your site? Go to the Settings tab and select the E-Commerce option. Here you can switch between PayPal and Google Checkout, change your e-commerce account info (if you need to switch to a different PayPal or Google account) and select a different currency using the provided drop-down menu (but only if you're using PayPal).