If you are looking for instructions on how to set-up the Shopping Cart within your site, there is a link within the Shopping Cart menu with some simple set-up instructions.
The instructions for the shopping cart can be found in the control panel under Commerce Shopping Cart Help
You can also simply use this URL:
This will take you directly to the instructional page.
(note: you will need to replace www.YourSiteName.com, with your actual site name for link to work)