What is it?

From the Amazon blurb:

Amazon CloudFront is a web service that gives businesses and software developers an easy and cost effective way to distribute popular content with low latency and high data transfer speeds. Like all AWS Infrastructure Services, Amazon CloudFront is a self-service, pay-per-use offering, requiring no long term commitments or minimum fees. With CloudFront, your files are delivered to end-users using a global network of edge locations. Amazon CloudFront works seamlessly with Amazon Simple Storage Service (Amazon S3), which durably stores the original, definitive versions of your files.

How does it work?

The CloudFront service is backed by usage of S3. You store your content in an S3 bucket and register the bucket with the CloudFront service. This creates a 'distribution' of the content you have registered. A distribution has a unique domain name associated with it you can access your cached content - you can also map your own name to this via a CNAME record.

When users request content via this distribution, they will be automatically routed to the nearest Edge location to retrieve the content.

The API

As with the other AWS tools then you will need to add it to your account.

The Getting Started Guide and Developer Guide give you all the details you need to use the service via the API.