Every AWS service will have resources associated with it. Resources can be thought of as objects within a service, upon which some operation can be performed. For example, an S3 bucket is a resource. Users can create a bucket, delete a bucket, and so on. An EC2 instance is another example of a resource. Users can launch an instance, stop an instance, terminate an instance, and so on. 

Depending on the service, you can have a number of operations on a resource. An EBS volume will have snapshot operations, AMI operations, and other operations attached to it. The actions that can be performed on a resource are clearly documented. If the user tries to perform an unrelated action on a resource, the action will fail.