Well, without indentation your code is difficult to read. Try wrapping it in <c></c> tags and format it to be readable by those unfamiliar with it. From a quick glance there are many errors (such as putting a \n after the semi-colon. Using warnings will catch that.)

That being said, try (actually, don't try it -- just get inspiration from it :P)

#!/usr/bin/perl 
use warnings;
use strict;

my @final; # Joined lines will be in here

open(URLS, '<', 'urls.txt') or die $!; # I can never remember if < is 
+read
chomp(my @urls = <URLS>); # Every line of URLS is a different element 
+in @urls
close URLS;

open(CODES, '<', 'data.txt') or die $!;
chomp(my @codes = <CODES>);
close CODES;

foreach my $url (@urls) { # For every element (line) in @urls,
    foreach my $code (@codes) { # and for every element in @codes,
        push @final, $url$code; # append the two and push it into @fin
+al
    }
}
[download]

The first three lines should be in all your Perl programs. Using warnings will catch a lot of stupid mistakes you will make and using strictures will keep you from making a lot of stupid mistakes. I think the rest of the code is self explanatory.

Updated with more comments.

Update 2: Ikegami reminded me (thanks ikegami :D) that you must chomp() each element of the arrays before you push it into @final to remove the newline at the end. I'll update my code to show this soon. Done (with inspiration from kyle :P).