About Login and Pay with Amazon for Magento
The Login and Pay with Amazon for Magento extension adds two components to your Magento installation:
To enable this feature, you need to create an Amazon Payments merchant account. The Amazon Payments account is where you find the access keys that you need to configure Pay with Amazon, and is also where you configure your deposit account so that you can receive payments, and where you can view reports. As a first step, please follow the instructions here to install the Magento extension via Magento Connect. Then, register for your Amazon Payments account by clicking the "Get started with account registration" button found under the Login and Pay with Amazon section in your Magento Admin panel.
More information about Login and Pay with Amazon for Magento, including pricing, can be found at Pay with Amazon for Magento.
Note: Login and Pay with Amazon is not the same as Checkout by Amazon (CBA) or Amazon Flexible Payment Service (FPS). If you have accounts with either of these older services, you still need to register for a new Amazon Payments merchant account to use Login and Pay with Amazon.