Computer networking deals with planning, implementation, and maintenance of computer networks. Computer network engineers are responsible for stability and integrity of voice, data, video and wireless network services.
CCNA is an entry level networking course from Cisco systems. It opens a various path in the field of networking. The career opportunities after passing CCNA are Network Engineer, Network Administrator, Technical Support Engineer, system admin, etc. If you are serious about your career then you should go for CCNP or CCIE for better job and money after getting some experience of networking.