The above answers are fine, but the below just seems more logical to me, and it doesn't use any weird modules:

#!/usr/bin/perl

my $i=0; #line number
my $j=0; #field number
my @array;

while (<DATA>) {
chomp;

my @colon = split(":");

$j=0;

$array[$i][$j] = $colon[0];

my @commas = split(",", $colon[1]);

foreach my $field (@commas) {

  $j++;
  $array[$i][$j]=$field;

}

$i++;
}

## Just for printing

my $a=0;
my $b=0;

foreach my $fields (@array) {
  
  $b=0;
  foreach my $field (@$fields) {
    

   print "FIELD ($a,$b) = " . $field . "\n";

   $b++;

  }

  $a++;

}

## End printing section

__DATA__
COLUMN_A: "Y","N"
COLUMN_B:
COLUMN_C: "something", "something else", "and more"
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