What is a cisco router? Why do we use it?

Routers are boxes dedicated to routing packets. For high speed connections, or multiple connections, they are useful. For small networks, the cost might not be worth it. They can also often handle many different routing protocols, rather than loading your PC. Routers also support a variety of network interfaces (ethernet, token ring, etc.) -- you can get what you need.
PCs are also used as routers, especially for small networks, and we will be working with PC routers more. However, due to popular demand we now have this session on configuring Cisco routers.