VPN is a term one hears often these days. However, while many people have some ideas about what it is used for - secure access, for instance - many probably lack vision of how they could benefit from its use. So for starters - what is VPN? You can use the Wiki link for a formal definition but in a less formal way one can define it as a network one can build to their own design provided one controls the server and the other machines one intends to network together have the capability to access that server via the internet.
So let us say you control a machine on the Internet with a public IP address. On it you can install a VPN server process. Then you can issue authorization to those you want to allow to join your VPN network.
Let us consider a practical example. I configure a server to serve a VPN with a private network defined as 192.168.20.0/255.255.255.0. Let us say the server gets the virtual IP address of 192.168.20.1, with the other addresses (192.168.20.2-254) available for grabs. So let us say my laptop gets an address of 192.168.20.2, my home machine gets an address of 192.168.20.5 and my office machine gets an address of 192.168.20.10.
Thus - using the same network protocols - I can collect the video feed off of my home computer to see what is going on at home, print to my office computer's printer - and do all of it from a WiFi point half the world away using my laptop.
Or - let us say - in addition to my office in Boston I decide to get one in Buenos Aires. No problem. I get another machine there - let's say, with a virtual IP address of 192.168.20.15 - and use it and the one at my office in Boston - 192.168.20.10 - to link the two networks. Now they are linked - via the internet but at the same time utilizing the VPN's security which is normally considered an unrbeakably secure way to communicate.
Those are just a couple of possible usage scenarios. I will try to cover this topic in more detail later on. For now just think of the VPN as a network you can define the way you like no matter where the computers who will join it happen to be geographically and topologically. So long as they have access to the internet and you allow them to join your VPN they can do so.