Router serves to divide two or more networks, but in fact Router is a networking device that is used to divide the members of the network protocol to another, with the router so a protocol may be sharing to other network devices. Examples of its application is that if we want to divide the IP Address to members of the network then we can use this router, the router features is the facility DHCP (Dynamic Host Configuration Procotol), by setting up DHCP, then we can divide an IP address, other facilities of the Router is presence of NAT (Network Address Translator) that can allow an IP address or a shared internet connection to another IP address.
The router works in a manner similar to switches and bridges. The difference is, the router is a filter or filters data traffic. Filtering is done using a particular protocol. The router is basically a divider network devices are logical rather than physical. The router can select the best alternative path (best route for the transport of data.), If indeed there are several ways to achieve the goal or if one path to the destination is lost for any reason.
Routers work at the physical layer, data link and network layer, so it can not be used carelessly. Routers are generally at least connected to two networks. Two LAN or WAN to LAN and the network of an ISP (Internet Service Provider). Some DSL modems and cable modem also has router functionality integrated into it to allow multiple computers to form networks and directly connected to the internet. If the hubs, bridges and switches are a networking device then the router is an internetworking device.