A local network means a collection of two or more computers that are connected together via some medium it can be air (wireless) or cable.
Network security is a branch of networking that encompasses strategies, policies, and standard operating procedures that make the network secure from various threats like unauthorized access or misuse.
These policies are generally adopted and implemented by the network administrator. To secure your network you must have a well-defined and secure network security policy.
You must have standard and safe rules for allowing inbound and outbound communication in a network. You must secure your network from unauthorized users.
For this purpose, strict rules must be implemented to secure a network. You must use strong passwords to make a network secure.
You must use strong encryption to protect communications in a network. To protect your network from malicious programs and ensure network security you must use good antivirus and anti-spyware programs that have high detection rates and are equipped with the latest scanning techniques like behavioral detection and heuristics.
Apart from these security measures you must place all the servers and databases inside secure premises and must implement strong rules for communication outside the secure perimeter. Special measures must be taken to secure the network from natural disasters as well.