It is just grouping of IP addresses in a class C with a default subnet mask of 255.255.255.0 .For example 192.168.0.1 to 192.168.0.254(your LAN). If not for this grouping all IP addresses would have to have to be mapped individually for routing. So it is represented by network address of 192.168.0.0.This allows data to be sent to any node by just the network address 192.168.0.0.(for very large LANS networks)This means routing tables only need to know the newtwork address not all nodes(254) on LAN or network.
PS Then there is more info how the router finds node and so on ?