Not really sure this belongs in this board, but...
You use a program called Hamachi (or any other service like it, some use Remobo, but Hamachi is preferred by most) to connect with people. Once you join a network (or add a specific user as a friend in case of Remobo) you'll see their IP address and you'll be assigned an IP address. In RS, I believe the process is Game > New Game > Preferences > Host IP. Whoever is calling (aka the Guest of the game) will enter the Host's IP address in that box.
Good luck!