AWS Key Management Service
The AWS KMS Developer's Guide will walk you through setting up your first master key and using it with an AWS cloud service.
An easy way to start using AWS KMS is the console. Located in the IAM section of the console under Encryption Keys, this interface will walk you through setting up new keys and policies.
AWS KMS is supported in the AWS SDKs so you can easily make AWS calls using KMS as well as integrate KMS managed encryption into your own applications.