Ok.
Port forwarding is ONLY applicable if you're running some kind of NAT or PAT. You will find that confusing until I tell you that you'd only be doing this if one of the following is true (within reason, I'm not defining edge cases):
1. You have a home router (such as a Netgear DG834G, or a Linksys WRT54G)
2. You are connecting to another PC which itself is directly connected to the internet (i.e. a modem)
If you have a PC that connects directly to a modem, and you get a public IP address on your PC itself, then all you need to do is to open up the LFS server ports in any firewall that you may have. How you do this simply depends on the software you're running.
To tell if you have a public IP, you simply need to check the active network connections for anything not in any of the following ranges:
1. 10.0.0.0 - 10.255.255.255
2. 172.16.0.0 - 172.31.255.255
3. 192.168.0.0 - 192.168.255.255
If your PC does have one of these addresses, then one of the following is likely to be true:
1. Your ISP doesn't provide a public IP - in which case you are stuffed
2. You're actually fulfilling one of the requirements of port forwarding (listed above)
3. Your modem itself is using the public IP and is passing your PC a local address (acting as a very simple routing device) - consult your ISP and/or modem handbook to see if you can get around this. Usually you can't if they've done this
If you still don't get whats going on then you'll need someone who is reasonably technical to sit down with you and to explain it in person. Unfortunately some things are tricky to pick up from words alone.