my @array = [[1,2,3],[4,5,6],[7,8,9]];

##</code><code>##

my @array = ([1,2,3],[4,5,6],[7,8,9]); # Note parens.
# or
my $aRef = [[1,2,3],[4,5,6],[7,8,9]]; # Note aref, not array

##</code><code>##

${$aRef->[0]}[1]
# or
$aRef->[0]->[1]
# or the most common...
$aRef->[0][1]