A Virtual Private Network connects the components of one network to another. Using tunneling or public network, a Virtual Private Network as name suggests, safely and securely transfers information from one network to another system.
VPNs allow users working at home to connect in a secure fashion to a remote corporate sever using the routing infrastructure provided by a public Internet work.
From the user's perspective, the VPN is a point-to-point connection between the user's computer and a corporate server. The nature of the intermediate Internet work is irreverent to the user because it appears as if the data is being sent over a dedicated private link.
VPN technology also allows a corporation to connect to branch office to other companies over a public inter network. While maintaining secure communications.