Shopify API - add to basket

I'm thinking of using Shopify to manage my shop. I need to add the products to the website with the API.

http://api.shopify.com/

I can get the products and stocks with this API call :

http://api.shopify.com/product.html#index

But, then I would like to 'Add to basket' - I cannot see from the API docs how to do this. Once added to the basket - I'd like to get the basket contents so I can display something like...

"2 items : £130 - checkout"

I don't need a detailed answer - just point me in the right direction - thanks.