First, you need to read up on how to read files. Second, when you want to your code to look something up -- you want to lookup if a name is in the other file -- think of hashes. The following should be useful.

use strict;
use warnings;

my %fileA;
my %fileB;
my %users;

# Read in FileA.
open(A, "FileA") || die "$!\n";
while (<A>) {
   my ($name, $machine, $laston) = split(/,/, $_);
   $fileA{$name} = [ $machine, $laston ];
}
close(A);

# Read in FileB.
open(B, "FileB") || die "$!\n";
while (<B>) {
   my ($name, $password, $location) = split(/,/, $_);
   $fileB{$name} = [ $password, $location ];
}
close(B);

# Check for users missing in FileB.
# Merge records found in both FileA and FileB.
foreach my $name (keys(%fileA)) {
   if (!exists($fileB{$name})) {
      warn("$name was found in file FileA, but not in file FileB.\n");
      next;
   }

   $users{$name} = [ $fileA{$name}, $fileB{$name} ];

  #delete($fileA{'name'});  # not needed
   delete($fileB{'name'});
}

# Check for users missing in FileA.
foreach my $name (keys(%fileB)) {
   if (!exists($fileA{$name})) {
      warn("$name was found in file FileB, but not in file FileA.\n");
   }
}

# Do something with users.
# Specifically, display matches.
foreach my $name (sort keys(%users)) {
   printf("user %s\n".
          "machine:  %s\n".
          "last on:  %s\n".
          "password: %s\n".
          "location: %s\n".
          "\n",
      @{$users{$name}}
   );
}
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