I'm guessing that your computer is connected to a LAN somewhere. Are your buddies on the LAN? If so, you'll need to check your network settings to see what your IP address is. Mine is currently 192.168.1.100 but this can change because my machine is configured to ask for an IP from my router. If I'm not the first computer to start up in the morning, it can be .101, .102, etc. But since it is .100, I can send this link to anyone who happens to be on my LAN:
http://192.168.1.00
Now if you and your buddies are NOT on the same LAN it gets more complicated. If you just connect directly to a cable modem, you may be able to send them your external ip. by 'external' I mean the one given to your cable or dsl modem by the cable/phone company. You can find this one by going to http://www.whatismyip.com/ . Note that 'external' in this case is not some official term, just one I'm using.
If you are connecting to your ISP and are using a wireless router then you may need to configure port forwarding on the router. That's a bit more involved. You may want to consider visiting http://port-forward.com in that case.