The zivad sub gets one parameter 'mago' in the array @_, which is stores in my $animal as a result of the default use of shift. It is shifting the leftmost scalar in the array @_. The my $list variable does not store a list but a scalar, namely the value of the %list hash for the key $animal. then the scalar $list is returned and printed...

This should be clearer

my %hash = (
            pas => 'vau-vau',
            macak => 'mijau',
            krava => 'muuuuu',
            pile => 'pi-pi',
            mago => 'ia-ia'
            );
            
sub zivad {
           my $animal = shift;
           my $hash_value = $hash{$animal} || die  "no  animal";
           return $hash_value;
           }
print zivad('mago');
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Not that I would use those variable names but they give you an idea of what the variables contain.