You can find all the info you need at perlref and perllol. Here's a brief description, though.

When you have a reference to something, there are two ways you can dereference it. By dereference I mean "take the pointer to an object and return the object." You can prefix the reference with the data type indicator or use the dereference operator. For example:

my @array = ('cow', 'dog', 'cat');
my $ref_to_array = \@array;

my ($first, $second) = @{$ref_to_array}[0,1]; # prefix
my $third = $ref_to_array->[2]; # deref operator
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This really comes in handy when you have four levels deep of referencing and you need something at the bottom. Typically, the deref operator (->) is optional between multiple levels of dereferencing. For example:

my @LoL = ();      # empty array
$LoL[0] = [];      # ref to anonymous array
$LoL[0]->[0] = []; # another ref to anonymous array

# the hard way
${${$LoL[0]}[0]}[0] = 'Look, up in the sky!';
# the easy way
$LoL[0]->[0]->[1]   = 'It's a bird, it's a plane, it's...';
# the shortcut
$LoL[0]->[0][2]     = 'Superman!';
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Now that you have more information than you needed or wanted... In this particular example, Perl "Does What You Mean." When you write $LoL[5][3] Perl recognizes that there's no way to rewrite that to mean anything but what you meant to do in the first place. =) So it just assumes the shortcut.

That's probably the worst example of anything I've ever given. Go read the perldocs! {g}