From https://openvpn.net

The VPN server is the underlying component in OpenVPN Access Server that does all of the background work; routing, tunneling, encryption, user management, authentication etc.

Usually, you want to use a VPN server in order to level up your security. You could use public wifi access or other untrusted connection. In this case, the provider may track your activity (accessed sites), grab your passwords (for non-ssl services), ...

This article will explain how to configure an OpenVPN server, allowing it to provide private IPv4 and public IPv6 addresses to connected clients.