CCNA is a Cisco certification that validates an individual's ability to install, configure, operate and troubleshoot medium-size routed and switched networks. The exam covers topics such as IP addressing, subnetting, routers, switches, NAT, DHCP and much more.
So the answer to your question is both! The CCNA exam tests your theoretical knowledge of networking concepts as well as your practical skills in working with Cisco equipment. To prepare for the exam, it is essential that you have a strong understanding of networking fundamentals AND that you are able to apply this knowledge to real-world scenarios.
There are many resources available to help you study for the CCNA exam. For theory, we recommend reading Cisco documentation and other books on networking fundamentals. For practical skills, we recommend using a simulator such as Packet Tracer or GNS3 to build out networks and experiment with different configurations.