Please Help With PAC File

Hi I was wondering if any1 could help me set up a PAC file for foxy proxy? As I understand, a PAC file uses javascript to change your IP address based on certain conditions. I found this PAC file on the internet:

function FindProxyForURL(url, host)
{

// Plain Hostname check
if (isPlainHostName(host)) {
return "DIRECT";
}

// loopback
else if ( host == "127.0.0.1" || host == "localhost" ) {
return "DIRECT";
}

// Internal DNS Suffixs
else if ( dnsDomainIs(host, ".aaaaaaeu.com") || dnsDomainIs(host, ".bbbbbb.local") || dnsDomainIs(host, "ccc.de")) {
return "DIRECT";
}

// Internally Hosts Sites
else if ( dnsDomainIs(host, "webmail.aaaaaa-europe.com") || dnsDomainIs(host, "webmail1.aaaaaa-europe.com") || dnsDomainIs(host, "webmail2.aaaaaa-europe.com") || dnsDomainIs(host, "erooms.aaaaaa-europe.com") || dnsDomainIs(host, "pdmworks.aaaaaa-europe.com")) {
return "DIRECT";
}

// Internal IP Ranges
else if (isInNet (host, "10.0.0.0", "255.0.0.0") || isInNet (host, "193.132.112.0", "255.255.255.0") || isInNet (host, "163.49.0.0", "255.255.0.0")) {
return "DIRECT";
}

else {
return "PROXY webproxy.bbbbbb.local:3128";
}
}




Except the aaaaaaa, bbbbbbb etc. are supposed to be real URLs. Can some1 explain to me how this works. What are these URLs for? Does the PAC file find proxies from that site or something?

I was wondering if I could make it so it changes my IP every 2 minutes? Also, what type of file do i save a PAC file as? Thanks for your help!