you have to setup your PC, Router, and Firewall for access.
First the PC
right click on my computer select remote and check off the box to allow Remote desktop. Add the desired users.
Make any exceptions to the Firewall
You have to find the port forwarding section for your router, for example on my linksys Router I have to to Applications and Gaming section and create a port forwarding entry by setting the application which is Remote Desktop, Port number, by default is port 3389, TCP protocol and the local IP address of the desired computer, which would be something like 192.168.1.101. So we have told the router to forward any RDC connections to the computer with the IP address 192.168.1.101.
After that you need your Route-able IP address so from home, search for google whats my IP and you get your ISP provided route-able IP address. And you're done.
Anywhere you have internet access open remote desktop connection type in the Route-able IP address form your ISP, which is the address of your router, so you're trying to connect to your router, but since you configured your router to forward the connection to the PC behind the router, the router just relays the connection and your PC answers the call.