Hello,
Ok, think you've misunderstood the basic vpn concept.
Typically a vpn will be used in two situations.
1. A site to site vpn exists between two sites who wish to be securely connected (usually branches of a single company)
The site to site vpn means that when users in one site contact a system (like a mail server, a citrix server, a sharepoint server) at the other, the router running the site to site will encrypt the traffic and send it (securely) over the internet.
So site to site gives the impression of a private connection between offices.
2. The second is for remote access.
An office will have a vpn connection (could be hardware, could be something on a server) enabled. A windows server for example includes routing and remote access (RRAS) to make this possible.
A remote user (at home, in hotel at another site) uses a vpn connection to connect (again securely) through to the work network. Once connected they can then access their e-mail, work data and other things - as if they were on the network.
Your reference to facebook etc is not correct. Internet services would not work on vpn connections.
What you do want is when you visit these sites to be using https connections (rather than http) as these sites encrypt the data sent between you and the end server.
Hope this explains things.