You call find_year(), but you never print its output. For testing, you could start with:

for my $title (
    "Let's party like it's 1999",
    "If 6 was 9",
    "If 6 was 9",
    "Summer of 69",
    "Disco 2000",
) {
    print $title , " => ", find_year($title), "\n";
}
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I can see this print each line in the title and the  => bit shows the year being extracted (not sure that's the right word) from the title.

sub find_year {
    my( $str ) = @_;
    my $year;
    $year = $1
        if( $str =~ /\b((?:19|20)\d\d)\b/ );
    return $year
}


for my $title (
    "Let's party like it's 1999",
    "If 6 was 9",
    "If 6 was 9",
    "Summer of 69",
    "Disco 2000",
) {
    print $title , " => ", find_year($title), "\n";
}
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One thing I'm not sure of is, I've tried to integrate the info above so that I can use the $title from a csv file rather than titles typed into the script (as in the above example). I have attempted this below but it's not working. I'd appreciate if someone could tell me what exactly i'm doing wrong. I know I'm being prompted to learn which I'm happy to do, but I think I would learn faster if someone told me what I have done wrong in the piece of code below.

sub find_year {
    my( $str ) = @_;
    my $year;
    $year = $1
        if( $str =~ /\b((?:19|20)\d\d)\b/ );
    return $year
}

#get the title from csv3

open CSV3, "<csv3" or die;

while (<CSV3>) {

  chomp;

  my ($title) = $_ =~ /^.+?,\s*([^,]+?),/; #/ match the title
}

for my $title {
print $title , " => ", find_year($title), "\n"; }
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This second loop creates its own $title variable:

for my $title {
    print $title , " => ", find_year($title), "\n";
}
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What you want instead is to integrate that call to find_year into your while loop:

while( <...>) {
    ...
    my ($title) = ...;

    print "Have title '$title'\n";

    print $title , " => ", find_year($title), "\n";
};
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