How do you use Radmin 3.0 to connect to a computer over the internet?

Question

I am able to use my internal IP address to connect to my other computer over the LAN. However, I cannot connect to my computer that is not on my LAN. How would I be able to connect to this computer over the internet. Please give a VERY detailed response including exactly how I would obtain the external IP address. Also tell me what the "connect through host" check box is used for. Inform me of the exact firewall settings I need as well. Do all this and you will get best answer.