VPN (Virtual Private Network) is a network methodology that extends and provides secure access to a private network (eg CS department network) through a public network such as the Internet. That is, it creates a secure "channel" (secure tunnel) through insecure networks. "Client" devices connected to the VPN are considered part of the private network and thus have access provided by the private network. There are several protocols that create VPN networks with the most common being IPsec and SSH. With the installation and proper configuration of the special software on the personal computer, the user can have a secure connection to the network of the Computer Science Department. Throughout the connection, the user's personal computer behaves and operates as if it were connected directly to the Department's network through a secure encrypted channel. The VPN infrastructure of the CS Department is based on the OpenVPN open source software that uses the SSH protocol.
If you want more information about VPN, and instructions of how to install it on your own computer please advice: VPN user guide.