This wizard allows for easy setup of the basic Google Checkout feature. See here for a more detailed guide to Google Checkout and its advanced features.
Basic
From Configuration Menu, click Payment → Google Checkout Wizard
This window contains the bare minimum necessary to enable Google Checkout.
Setting this to Yes enables the Google Checkout feature.
Use Sandbox
Setting this to yes instructs the cart to only do test transactions, through the sandbox servers, for Google Checkout orders.
Advanced
This pane allows you to modify advanced settings involved with the Google Checkout feature. This pane should only be used by developers who are familiar with these settings and have good reason to change them. It is entirely possible to render Google Checkout inoperative by changing these settings!