Typical use of a VPN as some have mentioned, Allows you as the "client" PC to connect to the remote "server" and establish an encrypted connection to the server. You will have to log in using credentials that allow you to access the network the the server resides on. (Typically, your office). Once connected you are using you office network to go back out into the internet. You can also access shared network drives on the office network as well.
I doubt that you could use a VPN for online banking, Facebook, Etc., as that is a service they do not provide. So, even if you used a VPN to connect to your office, you're using your office network to go to the internet for anything. You mentioned you have no internet at home. That being the case a VPN would not work for you.
Thanks for the explanation, seems like a lot of people don't understand how they work, me included, and think it's some kind of magic tunnel. If a 'home base' server is needed then it's worthless to me. I'm also coming go the conclusion that the biggest threat is unsecured wifi connections as pilgrim mentioned above, which I will avoid like the plague from now on and just use my cell phone despite it's inconvenience compared to a laptop.