Routing is a network service that allows communication across sub-networks. A sub-network is a single broadcast domain and a single broadcast domain can be associated with a Virtual LAN configured across a managed switch network.

A routed sub-network is sized using the 'sub-net mask' parameter and presents a default gateway to the Internet 'IP' Protocol end points that reside on the respective sub-network.

IP packets, destined for end points on remote subnetworks, are forward to the default gateway to be routed towards the destination network. If a route exists between source and destination networks communication can commence.

I say 'can' rather than 'will' as routers also filter packets. This filter is called a firewall, router firewalls can drop packets to introduce an additional level of security to a network.