This plugin will generate an Signed URL to enable private content to be served through Amazon CloudFront. A CloudFront key pair has to be created to configure the plugin and the CloudFront distribution configured appropriately. Full details of this process can be found in the AWS documentation
This plugin does not manage the process of getting Media Assets on to Amazon S3 or modify the Domain name for AWS based media. In order to do that a plugin such as Delicious Brains' WP Offload S3 should be used.