> (1) What is meant by a "mirror"?httrack creates a mirror/static snapshot. not
a copy.

> (2) You say "check the firewall/antivirus
> permissions".  What am I looking for when I check
> them? Port numbers, or what?
Something on your machine is stopping httrack from connecting to the internet. 
it's your firewall/antivirus software. I can't help with that.