Remote Access help

Hi, I am running windows 8 professional on my home PC and running windows 8 home on my Venue 8 Pro. I downloaded the remote desktop app on my Venue and setup a connection to my home PC. It was very easy and worked (at least on my home network) Now the first time I tried to access the computer outside my home it says that it can't find the PC. Is the connection only good with me being on the home network? Do I have to install some third party VPN to access it?

I am not very familiar with windows, I have not used it at all since XP, so I am still learning

Thank you for any help here.