firewall
 

i was wondering if someone could explain what a firewall is i keep getting a message to check my firewall

If you don't even know what a firewall is then chances are that you either don't have one or are operating on Windows XP and don't know that it has an built-in one.
Well, check this to understand what a firewall is (and yes, I know that in Safari's favorites it's listed in the Kids section but I like that web site a lot, okay. So quit bullying me. Or I'll tell mommy)