Why use a VPN

[hargi]

There's been lots of talk recently on here about VPNs and most of you use them and know why.
However for a noob, why would you use one and when? And also how do they generally work.

So to start with say at home do you go through a VPN all the time or just when looking at "dwarfs with vacuum cleaners"?
How's it work with on line shopping etc.

Is it like a program that you start on your desktop and then everything goes through it, or is it logging into a website then going through there?

 

[hargi]

I think the question should have been how, or when do you use them.
Is it all the time when you are on line or just certain times.

Also dies your iSP know you go through a vpn