Express Check Out is very convenient if you want to ship your purchases to your default shipping address, and bill to the credit card that you have stored in your Yahoo! Wallet.
It's easy--just click on the Express Check Out button within a Yahoo! Canada Shopping merchants cart, review your Wallet info, and select your shipping option. When you click Send Order, your information will be sent securely and directly to the store merchant.
This option should not be used if you want to ship to a different address or bill to a different card. In this case, you should go through the standard check out process, where you can change anything different from your default Express Check Out preferences.