As has already been pointed out, your notation is a little off... In Perl, {} brackets usually pertain to blocks, anonymous hash refs, dereferencing of references, or quantifiers in regexps. Your notation should be [[1,2,3],[4,5,6],[2,3,4]].

Note that if you have code that looks like:

my @array = [[1,2,3],[4,5,6],[7,8,9]];
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You're actually creating an array whos first element is a reference to the datastructure. It is more appropriate to do one of the two following things:

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
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In any respect, you can dereference a LoL (or AoA technically) as follows:

${$aRef->[0]}[1]
# or
$aRef->[0]->[1]
# or the most common...
$aRef->[0][1]
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There's a great little cheat-sheet that tye put together called References quick reference. Check it out! :)

You can also get a lot of good information out of perllol.