Help!!!

I'm a complete computer moron! I downloaded Limewire and it keeps saying Disconnected/ No files available. I read a previous post that said they were also having this kind of problem but the responses are beyond my Mac knowledge. I really don't know what a URL is or a Port. So I need someone who can explain to me how to figure all of this out! PLEASE HELP. I have an iMac with an OSX, and I think I'm behind a firewall to boot! Can anyone help me?