Network Access Control is not a precisely defined term such as we would see from a standards body. Rather it is a loosely defined term that describes any set of methods that combine to control access to the network.
For instance, one could argue that the very basic port-security command is a form of network access control since we can use it to limit the devices that can connect to a given switch port.
Cisco ISE provides NAC in a much broader context, allowing us to incorporate context such as what device, which user, what location, what is the posture status of the device, time of day etc. all in the process of authorizing network access and also including fine-grained control over what type of access in the authorization result.
How to configure NAC in the case of ISE is the subject of numerous how-to guides and far to lengthy to describe here. You can have a look at the extensive prescriptive deployment guides posted elsewhere in the community. Start here:
https://community.cisco.com/t5/security-documents/tkb-p/4561-docs-security
and search for "descriptive deployment guide".
