Go to
http://www.whatismyip.com .. This site shows you your IP adress
If you're at school and want to connect to home, enter your home IP adress and voila.. (if you have configured it Okay)
If you have a DYNAMIC ip, DHCP Leased -> changes once in a while, it's kinda irritating.. at
Dyndns.org you can create a free "DynDNS" , this is a hostname (yourname.dyndns.org for example) which forwards everything to your home ip... With a special DynDNS client you can update your ip, in order to keep your hostname working...
Good luck
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