Router groups

Basically, any device attached / interfaced to a port of a router, ie, hubs, routers, PC?s, and PC?s connected to those hubs and routers, are considered in a separate group and need to have a unique IP address?right? And that the NICs and their associated TCP/IP IP address groups have to have a IP address with the 3rd octet being unique of the other group, ie, the LAN group=192.168.1.5,6,7,8 and the WAN (internet) group=192.168.2.5,6,7,8? Is this correct?