Math::Matrix returns an object, and you can use arrow syntax to access individual elements:

use strict;
use warnings;
use Data::Dumper;

use Math::Matrix;
srand(time);
my $a = new Math::Matrix ([rand,rand,rand], 
                          [rand,rand,rand], 
                          [rand,rand,rand]);
print Dumper($a);
print $a->[0]->[0]; # get 1 element

__END__

$VAR1 = bless( [
                 [
                   '0.83428955078125',
                   '0.442596435546875',
                   '0.792205810546875'
                 ],
                 [
                   '0.193817138671875',
                   '0.21514892578125',
                   '0.23980712890625'
                 ],
                 [
                   '0.09869384765625',
                   '0.627197265625',
                   '0.514892578125'
                 ]
               ], 'Math::Matrix' );
0.83428955078125
[download]

It is often helpful to look at the tests provided with the CPAN distribution to see example usage code (follow the MANIFEST link to the "t/" links). In this case, the tests do show how to access individual elements.

Super Search is another efficient way of finding answers with code samples:
accessing elements inside Math::Matrix