my @a = ( 1, 2, 3 );
my %h = ( a => 1, b => 2, c => 3 );

# take a reference to the array
my $aref = \@a;

# take a reference to the hash
my $href = \%h;

# access the entire array through its reference
my $elem_count = scalar @{ $aref };

# access the entire hash through its reference
my $keys_count = keys %{ $href };

# get a single element through the array reference
my $element = $a->[0];

# get a single value through the hash reference
my $value = $h->{ a };

# assign to a single array element through its reference
$a->[0] = 1;

# assign a value to a single hash key through its ref
$h->{ a } = 1;