Before a resource may be used, an instance must be created. An instance is associated with actual system resources. For example, a Network resource may define a port range, but not an actual IP address. There might be hundreds of IP addresses available. Only when the resource instance is created is an IP address actually assigned.
Once the instance is created, the system resources are owned by the contract used to instantiate the resource. The resources will not be released until the resource is released or the contract is terminated.