A router is an easy way to network your computers, allowing them to access the Internet through a single connection/IP address. Some also provide firewall and printer-server capabilities.
A Router allows you to create a network, by separating an existing network, this permits you to share your Internet access without being dependent on one computer's connection
Providing individual internet access to each computer on a network can be costly and hard to manage, the use of routers allows for greater efficiency.